I'm on my girlfriends laptop and its web browsers are acting very oddly. When scrolling down a page, it seems like the refresh rate on the monitor drops to the point where the screen is redrawn quite like lowering a window shade.

Checking system resources, any time you scroll, the CPU usage jumps from 0% to 100%. What could cause this? It happens in both IE and Firefox, virus and malware scans come back clean.

Its an HP Pavilion ze5500. Its a 1.5ghz proc with 512 meg of ram. It shouldn't have problems scrolling a fricken web page.