If you're running Internet Exploder under Windows (any version), that's very likely the problem. A lot of MS software behaves badly under heavy loads.
If you haven't already done so, install Firefox and Opera and give both of them a trial. Or even take the plunge, install Linux, and leave MS behind forever. I started using Ubuntu Linux in summer 2007 and now rarely use my Windows machines at all. It has its moments, but if you get into trouble there are endless online resources to help you resolve your difficulties.
Someone else suggested you may not have enough memory in your computer. RAM is cheap, so if there's room for adding some, do so; there's nothing like lots of memory to make a computer run better.