Go to this site http://www.theeldergeek.com/ and use the search box at the top, type the name of the service in and it gives you a break down of if you need it or not and explains what it does.

Also consider downloading a program called CCleaner and running that against your PC using default settings. It'll clear out all your temp and history and any other crap it finds.

Check your Add/Remove programs icon and remove programs you don't use.

Cheers

Matt