i have found that a lot of members has posted registry tweaks even i have posted some 

Can some one tell me how you people get an idea of where to crete a DWORD, where to create a STRING etc   even what value you should give them

what i did is i understand the working of some applications like tuneup ultility TWEAK XP etc and this helps me in getting registry tweaks

even all of my registry tweaks came from this method only

WHAT U PPl DO??????? 

thankz vasu for replying, just read the following registry hack

To increase/decrease the thumbnail size and quality just open Regedit and
navigate to
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer
Now create two DWORD value named
ThumbnailSize and ThumbnailQuality and give their value as you wants. I
recommend ThumbnailSize=225 (decimal) and ThumbnailQuality=100 (decimal)

in the above hack two DWORD values are been created ThumbnailSize and ThumbnailQuality can you explain me how some one get the idea of creating a DWORD value having the name ThumbnailSize and ThumbnailQuality

hope you might get understood what i am saying

Most of the times we find these keys and values by decompiling system files but its not an easy task.