Buffalo Bad Asses

Try adding these lines to your autoexec.cfg

set r_mode -1
set r_customwidth 1600
set r_customheight 1200

Set 1600 and 1200 to whatever resolution you are trying to get.

Which MemTest did you use? I generally use the one found here: http://hcidesign.com/memtest/, it doesn't require you to put it on a disk. If it stops at 0%, try telling it to allocate less RAM. If it just stops without any error dialogs, that probably just means you're telling it to allocate more RA...

Have you recently installed any new hardware or drivers? If so, that might be causing your problem, and you should try rolling back the drivers. If not, you might want to test your RAM with something like MemTest to see if it is corrupt.