Macbook freezes when scrolling in any browser

I've searched high and low but can only find info on the macbook pro touchpad problem, which this is not.

Basically when I scroll down a webpage in any browser (Firefox or Safari) the browser sometimes quits, sometimes freezes or I get dumped back at the login screen. This also happens if I use the scroll bar or even attach a mouse and use the scroll wheel! I did a disc check and repair and even resorted to re-installing Leopard...all to no avail.

Does anyone else have this, know a fix or can shed any light on it at all? If it's a known issue, I'd like to read more about it as it's really bugging me. Maybe I should take it back to the Apple store?

Thanks