I've got a Sapphire Toxic Radeon HD 4850 512MB
DXDiag and Blizzard's beta system scanner are both showing me 244MB of video memory. GPU-Z and my display settings show 512MB. I'm not sure if the system is utilizing the full 512MB or not.
I was previously running WinXP pro (32bit) and the full 512MB showed up fine everywhere. I just installed a new motherboard, CPU, ram, and did a fresh install of Windows 7 Home Premium on a new HDD, and now this issue has appeared.
I've tried both the 11.9 drivers, and the 11.10 preview version, which I believe was released to give better Battlefield 3 beta performance.