Vista needs 2 gigs of RAM for good performance. You could get by with 1 gig but it limits how much you can run at the same time and the effect the fancy Aero graphics have on your system.
Vista Home Premium is not a basic version. Vista Home Basic is. It does not include Aero or the Windows Media Center, Windows Mobility Center, and several other features. Seehttp://www.microsoft.com/windows/products/windowsvista/editions/choose.mspx
I have three gigs on my XP/Vector machine. Why not? RAM is very cheap these days and the more, the better. Vista is not suitable for older computers, period. New Vista computers should but often don't come with enough RAM (or more can be added if they don't). My Vista laptop came with 2 gigs and it's been enough for everything I run at once, including a virtual machine.