Just a thought,but have you thought about disabling startup items that you don't need to start on bootup.Having too much stuff in there can slow your system down dramatically.The only things I allow to start on bootup on my machine are my anti virus and firewall.
Also go here:
http://www.blackviper.com/WinXP/servicecfg.htm
and check out the service configurations,there are a lot of services that you can disable to help your system run better and faster
Another thought,but before running ANY scan for virus,trojan,worm etc. you should ALWAYS turn off System Restore as copies of everything you are trying to get rid of are in System Restore just waiting for you to put them back where they came from in the first place.
Another good thing to do before running the scans is to clear out your TIF and other temp files.
In Internet Options, under the General tab click the Delete temporary internet files, choose to delete all Offline content.
Also, go to Start - Search - Files or folders - in the named box, type: *.tmp and choose Edit - select all - File - delete.
Empty the contents of the C:\Windows\temp folder and C:\temp folder, if you have one. Empty Recycle bin.
Once you have cleaned your system and have it running the way it should,turn System Restore back on.