well I am not sure about the graphics card, and frankly I am not sure about the RAM either, but could it be at all possiable that you may not have all you ram slots enabled? I've encounterd this problem a few times with older computers, and by older computers I mean like bios 2 or a very very early bios. honestly I am not hardware literate.
I've seen this question before on this forum. I'm not sure what method MOH uses to scan your PC but it could be that it won't pick up over 64M of card RAM .I don't believe the 128 cards were out when they wrote the scanning program. Just a thought.