I have to agree with telboy - I have never had any time for the Norton Suite of Apps, and that in combination with and AOL software is a marriage made in hell in my opinion.
It may be worth uninstalling norton (if you are only using the anti virus stuff, then try AVG, it is free for home use, and as good as any commercial software), and seeing if things improve.
Other than that, I would say the most likely cause is memory, you can replace memory for about £20 per 512Mb, so if removing Norton does not improve things, then I would test and replace if necessary the memory.
Cheers
Dan