While currently there are no graphics cards with that lot of memory onboard, they are likely to be available in future and it may appear that in not too-distant-future.
ForceWare 66.93 drivers released on the 9th of November, 2004, correct certain bugs, are designed to improve performance in 3D applications and also enable NVIDIA’s programmable video processor. Additionally, the new drivers contain a number of enhancements, such as support for GeForce 6600, GeForce 6600 GT, and GeForce 6200, SLI multi-GPU configurations, HDTV use over DVI connectors, advanced DVI timing on all GeForce 6 series GPUs, 512 MB frame buffer GPUs and some more capabilities.
More info at X-bit Labs
NVIDIA’s New Driver Tips 512MB Graphics Cards
