CPU Usage stays at 100% when web browser is open?

32 Bit Vista Home Premium

4GB Ram

Intel Dual Core E2180 Processor @ 2.0 GHz

Avast Antivirus

Internet connection via wireless card

I can have everything else that I normally have open and it doesn't seem to matter, and I don't think it's the internet connection in general because I'm still able to download things from iTunes in a reasonable amount of time usually it seems to be connected to having a web browser open.

Also it doesn't seem to matter which one, I can be using a different browser (Firefox/Safari, etc.) doesn't seem to matter, and the same thing happens

It will work well for the first few minutes usually, but after that it will peg the CPU usage at 100% and cause the browser to just freeze constantly, some times it will come back out of it in a relatively short period of time, and other times it just says spinning on itself indefinitely

I don't have a lot of other things open, and I've already run the disk cleanup, updated and ran the antivirus, run the check disk, and other things I could think of but haven't gotten there yet.

The only other thing that seem to possibly factor in, is that one of the other computers in the house, a laptop, tops out at 802.11B, while the rest of the network is 802.11G, I think I can attribute some of this to that laptop slowing the rest of the network down, but I'm thinking there has to be something else as well.

Any thoughts on what might be causing this, and more importantly what I can do about it, are appreciated.