Incidentally, I see this streaking and coloring in the BIOS setup as well. Is there something basic I am missing ? I have swapped it with another exact similar card too.
If it happens before you get to an OS, it's a hardware problem somewhere, period. If you swapped the card and it still happens, it's almost certainly a motherboard issue. There's a chance that it's a PSU issue, but I'd be surprised. Make sure everything is configured correctly in the BIOS. It sounds like the memory on the card is bad; however, that shouldn't happen with another card. It could be the AGP slot on your motherboard is faulty (or your motherboard is just dying).