TeamBundy: Another thing which will make a PC "freeze" for short time is if your hard drive is fragmented a lot - so a good defrag always helps.

(For those that don't know - if a hard disk is not defraged, pices of data on the hard drive can be split up in many parts - which takes longer for the PC to read - which in turn, slows things down and can cause "freezes" when the PC can't get it's information fast enough)