Add/Remove Programs - Programs and Features
This is the first place you should go when cleaning the junk off of your computer.
In Windows Vista and Windows 7, the location is called Programs and Features. Likewise to get there, to go the Windows Button - Control Panel - Programs and Features.
In either case, this area of Windows lists all the programs on your computer that were more or less legitimately installed there (and probably a few that snuck their way in without you knowing). Remember, this is a list of programs installed in Windows, not necessarily a list of programs running all the time. But the reason this should be checked right away, is that many programs that are installed in Windows do have components that load up immediately when Windows starts (before you ever launch the program). So, if you're not using the program and not planning to use the program, you might as well get rid of it. This may get rid of a few startup items along the way.