Two things you also need to be aware of...
(1) Norton 2005 is not a good antivirus program. It eats up spare memory resources, and isn't that good at its job. You're better off with a free antivirus program like "Avast!" or the LATEST version of AVG free. If you would like to pay for the best Antivirus there is, you should get NOD32
2) Using system restore is a bad idea if you ever suspect there's a virus as the virus will hide in the system restore files. A much better way is to back up all your important files onto CD/DVD and then you know you have a "spare" copy of these files and would just need to reinstall them if you do need to reinstall windows.
3) Reinstalling windows every so often (say every 6-12 months) is often a good idea anyway - even Windows XP is pretty poor at "housekeeping"
4) Highly recommended is "Crap Cleaner" which is what I use on both my own PC and those of my customers when I want to get rid of rubbish.