The Mobo is a budget version, and does run slow, but will support up to 8Gb of Ram. Try another stick to take it to 3Gb. Delete all .tmp files, delete all temp Internet Exlorer files. Defrag the HD. Stop all rubbish running at start up (my way, not necessarily everyone's way) by running MSCONFIG from the Start/Run/msconfig, and untick all the rubbish that starts on boot. Google is your friend to confirm or deny.
As has been stated, you should be running XP SP3 (if not, why not?)
Backup all the files you would miss, if they suddenly disappeared, to the external HD. Then burn to a R/W DVD, then make a second copy to place somewhere else... just in case. Backup emails/contacts/etc...
Variations on a theme for those with a different view
