I was reading the release notes (ya, i'm bored) for the newest Nvidia drivers and found the following:
GeForce 8800 GTS 320MB: The driver reports incorrect video memory (256 MB) in
the Windows Vista Display Properties panel. 
However, the NVIDIA Control Panel properly reports the dedicated video memory as 320
This still doesn't answer my question if the full memory is being utilized or not?
Anyone know of a way to check?