Shoutbox

On Windows XP Professional (not sure about which editions of Vista/7 this works on) you can use taskkill.exe to terminate a process. You can also use net stop to stop services and net start to start them (on any edition of Windows).

Also, take a look at this: http://www.iobit.com/gamebooster.html
It stops services/terminates processes that you probably don't need while gaming.