If you want to test an explorer shell plugin or registry hack without having to log off, more technical users will usually just kill the explorer.exe process in Task Manager. Windows Vista has another way to do the same thing that you might not be aware of.
This tip was sent in by Justin, one of our most active forum members.
Alternate Close Explorer Method
Open the Start menu and then hold down the Ctrl and Shift keys at the same time. Right-click on an empty area of the menu, and you'll see a new option called "Exit Explorer"
The taskbar should completely disappear, and any open folder windows if you are using default explorer settings.
Classic Close Explorer Method
Pull up Task Manager with Ctrl+Shift+Esc and then right-click on explorer.exe in the process list, and choose End Process.
Restart Explorer
Use Ctrl+Shift+Esc to bring up Task Manager, and then go to File \ Run and type in explorer into the run box.
The start menu will re-appear, but you might notice a few tray icons will be missing until you log off and back on. (or restart those applications)
The only real benefit to using the alternate method is that Explorer has a chance to properly shut down, rather than just killing the process which could screw things up. Also, it's fun to know these hidden tricks =)
http://www.howtogeek.com/howto/windows-vista/hidden-trick-to-close-windows-explorer-in-vista/