Badcell, thats the tricky question

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A clean Windows install usually has 19-23 processes.
First thing id do is: Check the Software Add/Remove for programs you dont use/need and uninstall them. Then check the Autostart folder in your start menu and remove all programs that you dont need running all the time.
Check all the Programs you have installed for autoupdating features (its best to disable them, less processes and less traffic on the connect in the background).
Check the Stickies in this Forum. Skuzzy posted some hints and tips how to tweak your system for better performance.
If you have processes that you dont know what program they belong to/what they do, do a google search for them.
If you want to reduce processes to a minimum for gaming, id recommend programs such as FSautostart.
One word of caution though: If you do not have much experience with computers, better check and double check before closing a process. When in doubt, ask.
Hope this helps you.