The following programs are 100% free.
First, you will probably want a firewall, to keep all those nasty bugs from getting onto your computer.
I suggest you use any of these.
Firewall
ZoneAlarm. - I think this one is the best out of them all. It is easy to use, and i've always used it.
(ZoneAlarm is designed to protect your DSL- or cable-connected PC from hackers. This program includes four interlocking security services: a firewall, an application control, an Internet lock, and Zones. The firewall controls the door to your computer and allows only traffic you understand and initiate. The application control allows you to decide which applications can and cannot use the Internet. The Internet lock blocks Internet traffic while your computer is unattended or while you're not using the Internet, and it can be activated automatically with your computer's screensaver or after a set period of inactivity. Zones monitor all activity on your computer and alert you when a new application attempts to access the Internet. Version 6.5.722 removes McAfee installation gate and fixes an update problem with LastWriteTime.)
Your Windows Firewall. - Keep this on at all times, it will give you that extra security.
Jetico Personal Firewall. - This firewall is allright. It does it's job.
(Jetico Personal Firewall protects your computer from unwanted hacker's attacks from outside as well as from malicious programs living secretly inside your computer's memory and hard drive. Three levels of protection are included: low-level network packets filtering, application-level network events filtering, and filtering of user-level process activity. Jetico Personal Firewall checks every packet that comes in or out of your computer.)
http://www.jetico.com/index.htm#/jpfirewall.htm
Sygate Personal Firewall. - I've used this before, and it's pretty good. Probably my 2nd best firewall.
(This firewall automatically protects your PC from hackers and other malicious attacks. It includes full-ICS support, protocol driver-level protection and enhanced logging.)
http://www.tucows.com/preview/213160
I don't see the point in posting a million firewalls to use, because you really only need one.
Anti-Spyware
Spybot Search and Destroy. - I use this the most, because it works very well. It's user-friendly, and has a few options.
(Spybot - Search & Destroy can detect and remove a multitude of adware files and modules from your computer. Spybot also can clean program and Web-usage tracks from your system, which is especially useful if you share your computer. Modules chosen for removal can be sent directly to the included file shredder, ensuring complete elimination from your system. For advanced users, it allows you to fix Registry inconsistencies related to adware and to malicious program installations. The handy online-update feature ensures that Spybot always has the most current and complete listings of adware, dialers, and other uninvited system residents.)
http://www.download.com/Spybot-Search-Dest...4-10122137.html
Adaware. - Great program. Again, it's easy to use, and has some good features on it, oh, and it works well 
(With the ability to scan your RAM, Registry, hard drives, and external storage devices for known data-mining, advertising, and tracking components, Ad-Aware SE easily can clean your system, allowing you to maintain a higher degree of privacy while you surf the Web.
Ad-Aware SE Personal Edition boasts a number of improvements. Extended memory scanning now scans all modules loaded by a process. Scanning uses the all- new CSI (Code Sequence Identification) technology to identify new and unknown variants of known targets. Extended Registry scanning now scans Registry branches of multiple-user accounts and performs additional smart checks to detect dynamically created references. Scanning speed is noticeably faster, and this version offers an Extended Scanning mode for known and unknown/possible browser hijackers.)
http://www.download.com/3000-2144-10045910.html
AVG. - Another great and easy tool to use. It updates quite a lot, and it's one of my most used Virus scanners.
AVG Anti-Virus Free Edition is a free anti-virus protection tool developed by GRISOFT for home use. We invite you to join the millions of satisfied customers worldwide who have downloaded the software and now enjoy the benefits of AVG Anti-Virus Free.
http://www.softpedia.com/get/Antivirus/AVG...e-Edition.shtml
BitDefender. - I havn't used this much, but i've heard from people that it's pretty good.
Much more than an AntiVirus product, BitDefender 9 Professional Plus ensures unmatched antivirus protection as well as data confidentiality, active content control and Internet filtering. The Professional Edition of BitDefender protects users’ data on all levels, both in an office environment and at home. BitDefender Professional is an ICSA Labs, Virus Bulletin, Checkmark, TUV, and Checkvir certified solution.
http://www.filehippo.com/download_bitdefender/
Hijackthis. - This is a good program, very good indeed.
HijackThis lists the contents of key areas of the Registry and hard drive--areas that are used by both legitimate programmers and hijackers. The program is continually updated to detect and remove new hijacks. It does not target specific programs and URLs, only the methods used by hijackers to force you onto their sites. As a result, false positives are imminent, and unless you're sure about what you're doing, you always should consult with knowledgable folks before deleting anything.
http://www.spywareinfo.com/~merijn/downloads.html
Pop Up Stoppers
PopUp Stopper. - This is a nice little program, it does it's job well.
Panicware's Pop-Up Stopper blocks pop-up ads in Netscape, Internet Explorer, and Mozilla. It can block Messenger Service and desktop ads, too. There's no need to adjust proxy settings or add sites to a list. Pop-Up Stopper will not strip Web images or slow your browser. You can allow pop-up windows when you want them. User settings allow various pop-up notifications, such as flashing icons or new, fun sounds. Simply hold the Ctrl or Shift key to allow selective pop-up windows; but most new links should open automatically.
http://www.panicware.com/product_psfree.html
Google Toolbar. - Although i use Mozzila Firefox (http://www.mozilla.com/en-US/firefox/) instead of IE, this is a good tool for you IE users.
Google Toolbar enhances Internet Explorer with a Google search box and other useful tools like a pop-up blocker, web form filler, and spellchecker. With the new Google Toolbar beta, you can add buttons and bookmarks, get instant search suggestions, and share web pages with friends via email, blog, or SMS. Google Toolbar is free and installs in seconds.
http://www.download.com/Google-Toolbar/300...4-10056938.html
A good Setup
Persinally. This is what i would use for my setup on my computer.
Zonealarm. - Running at all times.
Adaware. - For Scanning Viruses
Spybot. - Also for scanning viruses
Panicware's Pop-Up Stopper. - Mainly just for Mozzilla, so you don't get annoying popups.
I also use NOD32, but that's not free.
I would do a computer scan every 3 - 4 days to make sure no viruses are on your computer, and also, before opening files. Scan it with this Free Online Malware scanner.
http://virusscan.jotti.org/
I hope this guide helps some people.
Myth - "You can get viruses using p2p"
Reality - The probability of getting a virus using a p2p program is the SAME with getting a virus from web if not lower. Actually if you use IE to browse the web with no security enhancements you can get more bad stuff.
Myth - ''You can be hacked using a p2p program''
Reality - And if i don't use a p2p program i'm not going to be hacked ? Some kind of magic umbrella is going to protect me if i will not use a p2p program ?
Myth - ''The p2p networks are loaded with spyware/viruses/adware and other bad stuff''
Reality - If someone is going to download ''Adobe Photoshop Gold Premium'' from Kazaa and the file size it's about 30mb be sure that's a virus and a big one. Also if you are going to download a ''FREE'' screensaver or some ''download boster'' from Download.com the probability of getting you pc infected is the SAME with getting bad stuff from p2p if not HIGHER.
Myth - ''P2P is illegal''
Reality - Please read this and this , as you can see P2P is legal in some country's and in some others not. P2P (file sharing) as definition is NOT illegal, otherwise open source programs like eMule, Cabos or BitTorrent should be closed, sharing copyrighted files is illegal in about 70% of the world country's.