Voodoo kernel panic on shutdown/restart + other issues

[Morose7]

I get a kernel panic every time I shut down, and when I open itunes it starts to sort gapless playback, and then stops responding.

Often the PC freezes, and video becomes distorted, not updating as it should do the image, so if i'm scrolling on say BBC news it'll show the top of the page when I've scrolled to the middle.