Screwy video cardFollow

I'm running a Radeon X600 256 MB series graphics card and for a while it's been a complete *****, whenver there's too much stress on the screen like functions being done at once the desktop freezes and then either reboots the computer or goes all slow and whenever i scroll or change the onscreen display by opening a folder or something it refresh the whole page.

Is this something to do with my drivers? or is the vid card just a dud? If it's the drivers could someone point me in the right direction of something to download?

Any help would be greatly appreciated, cheers.