Damn.
I KNOW ABSOLUTELY NOTHING!
Betrayed by OEM bureaucracy.
Even my 'Display Properties' said 256MB, as did '3DMark05' and 'dxdiag'.
LIES, LIES, LIES!

OK, since I'm 0 for 3, is the Ferrari 5000 at least a decent 15.4" notebook to game on?
Go ahead, make me 0 for 4.

You know: If the Turbocache actually does what it claims, wouldn't the System Memory decrease 128MB as the Video Memory increases?
For example, in XP, 16MB of shared video would report 16MB less System Memory. (i.e your 512MB of RAM would report 496MB because your AGP Aperature stole 16MBs) Shouldn't it be the same concept?
Then again, what the hell do I know.