Nvidia are introducing SLI architecture which allows TWO GPU's to be linked together in the same system running on the PCI Express bus, so you could have 512mb AND using TWO GPU's have a significant boost in graphics processing
Drool here:
Nvidia SLI
HIGH setting needs 256mb Video RAM not 512mb! You can also unpack the 5 pakxxx.pk4 files to help texture loading between areas, but you need an extra 3GB HD space