video memory

The device object should have a function:

device->GetAvailableTextureMem()

Thanks. Seems strange, though. MSDN says that the returned value is rounded to the nearest MB, but the results I are some large numbers (551550976).

551550976 is exactly 526 MB.

Remember that memory includes AGP memory, etc etc. There's no way to get the actual VRAM size from DirectX, there's been a tonne of threads about it in this forum. Have a look trough threads from the past week or two and you'll find several.