your system should only use some of the ram if you have an onboard display card enabled - as you say in your post after that:
if you take 1024 (1gb) and minus your 768 you get your missing 256mb
is your gpu onboard?
you're on the right track... you need to start simple to find where the problem lies. Often it is just somthing simple like updating drivers or software.
from the specs posted here the NVIDIA GeForce4 MX 4000 that Wasp has, Nvidia GeForce 6300 that UAWEA WOLF THE DESTROYER has, and the ATI Radeon 9100 that P-G News has doesn't look like it supports HW T&L which could be the cause of the blackness......
http://www.petro-gamers.com/games/uaw/system/ says you need hw t&l as a minimum as well as 128mb(256mb for online) on the gpu......
so UAWEA WOLF THE DESTROYER you should just scrape in there, P-G News may get away with it but prob not...... Wasp, I'm sorry, but seriously upgrade your gpu.
http://www.mgram.com.au/product_info.php?products_id=5845 $75 for a Nvidia GeForce 8400GS 256Mb
can you show me a screen shot of the error?