They both are 512mb sticks at 333mhz now. I really have no clue if it supports dual whatever. Im not still runnin the 256... i just didnt realize they were different speeds
until i went to replace it with a second 512
my vid card is a Nvidia Geforece 7600 GS OC.
if u wanna see the details i took a pic of it and posted it a while ago when i got it.
http://fallenangelsx.com/forums/showthread.php?t=2442