CPU Spikes 100%

Hello,

I just installed a clean copy of Windows XP Pro on a Dell Dimension 2400, Celeron 2.4GHz with 512MB RAM. IE was working good for a while but now when i browse to new websites, my CPU spikes to 100% and it takes forever to load a website. The only software I installed was Norton Antivirus 2004, and i do notice that is is not a problem when I DISABLE the antivirus realtime protection! What could be happening here? NAV2004 causing the problem?

Thanks,
Adam