m8 msconfig is probably the best prog to use, its lists all the programs that startup, if you dont know what a certain file is search for it on here
http://www.processlibrary.com/ it will tell ya whether its important or not.
Just click start - run - type 'msconfig' - click last tab called startup and have a look at what is starting up. I have only avg and ctfmon running.
You can also look at the srevices tab, click hide all microsoft services and it will show some that maybe you dont want running like norton, ipod, office software etc.
if you mess up you can always use system restore to go back a few days.