Beyond3D talked to Epic Games´ Tim Sweeney about the upcoming Unreal Engine 3.
“...Off-the-shelf 32-bit Windows can only tractably access 2GB of user RAM per process. UT2003, which shipped in 2002, installed more than 2GB of data for the game, though at that time it was never all loaded into memory at once. It doesn't exactly take a leap of faith to see scenarios in 2005-2006 where a single game level or visible scene will require >2GB RAM at full detail...”