well first of all i'd try to find out if that works? would your 5900 work as a 5959u with a 5950 bios??? I dunno i'd hope somebody would answer that question.
well, it could be that the drivers are not communicating with the hardware through the bios properly; thus, causing artifacts. I would try underclocking the card to a level at which you KNOW the card would not create artifacts because of clock speed. Then check for those artifacts, If you get these artifacts still- then we know that the drivers are not communicating with the hardware through the bios properly. I would first then remove the card from the computer, reinsert the card and attempt to make sure that it is properly in its slot. If you havn't tried this yet, I would underclock the card for this test. Underclock card, remove all evidence of nvidia display drivers, add/remove programs, delete nvidia registry key, delete any left over nvidia files. Then defragment your hard drive and install the newest nvidia driver. Rerun your tests underclocked. still artifacts? If you want to try some other version nvidia drivers its possible you are using bad drivers for the 5950u, maybe even drivers which existed before the 5950u was around? If all else fails i'd reflash the old bios before you do any serious gaming or benching with it at stock speed or overclocked, but it might be worth trying to get the 5950u to work.
Oh and first you might want to check how hot its getting!
maybe it needs better cooling?
