Better Safe than Sorry
ok..here is what i recommend to keep you pc a healthy one..
1: run an anti-virus
2: run a firewall
3: run spybot search&destroy
4: run ad-aware
5: update daily and not weekly

always scan your system from time to time to make sure your pc is in tip top condition.if you are a little paranoid like me,then you could erase your cookies and other temporary files daily.XP has a diskcleaner that does a pretty good job at that.If you arent satisfied then give TuneUp Utilities 2003 a try,but it's shareware.Means you gotta pay to use it but you could do some magic stunts so that you dont need to pay...ahahahha.LOL...shhhhhhh.