Acer Travelmate 800LCi graphics card problem

Hi,
I've got pretty new Acer. It was very cheap 'cause it's graphic cards memory is corrupted. So when you're trying to use it there are plenty of little pixels in wrong place and etc troubles. In winXP and Bios text is sometimes almost unreadable. But when I use Knoppix, there are very much less messy pixels.
Why is that? Does Knoppix use less graphic cards own(corrupted) memory and ram instead of that? If so, is there anyway that i can make knoppix use _ONLY_ the RAM instead that corrupted memory?

Thanks if anyone cans and wants to help. Sorry my poor english.

probably due to what colour depth you have the screen set at
more depth (24/32) you would use more memory

same with desktop size
800x640 would use a lot less memory than 1280x1024