Norton and McAfee are what my husband refers to as "Bloat ware" They slow your computer down as they run in the background. You could also have spy ware on your computer - do you get pop-up ads?
You can try AVG (anti-virus) for free:
AVG Free - Download antivirus and antispyware software for Windows XP and Vista
And Spybot for ad-ware and spy-ware:
The home of Spybot-S&D!
My husband the computer geek just walked in the room said upgrading to Vista is like "pouring gasoline on your house when it's on fire." HA. No Vista won't help you because unless you buy a brand new top of the line computer Vista will run slow. We have Macs, but your WinXP should work better if you run those programs and uninstall Norton.
You can also do a speed test at
Speakeasy - Speakeasy, Inc. - Broadband, Voice and Data Services to make sure your connection is consistent.
Good luck!