Operating system change

[subdude]

if i change to windows vista, what should i go for, home basic, home premium, business or ultimate? i only game on the rig so i don't need anything fancy.
and what about windows7, it seems that most people testing it prefer it to vista?

i read, that in order to use the full 4GB ram i have to have a 64 bit operating system, is that true and are all versions of vista available in the 64 bit option?

thanks for any help!