This is according to MS:
32-bit versions of Windows Vista Home Basic, Home Premium, Business, Enterprise, and Ultimate: 4GB
32-bit Windows Vista Starter: 1GB
64-bit versions of Windows Vista Home Basic: 8GB
64-bit versions of Windows Vista Home Premium: 16GB
64-bit versions of Windows Vista Business, Enterprise, and Ultimate: 128GB
You can get some good info here:
http://www.vistaclues.com/reader-que...windows-vista/