The
comparison chart that Microsoft has is pretty good.
The different version of Vista have different
system requirements. If Vista Home Basic is only offered than the PC has a less-than-spectacular video card. I reccomend staying away from Home Basic.
I like the 64 bit version because of the added security it has, but you
will run into compatibility issues with certain programs and hardware.
All of the different versions also have 'Anytime Upgrade' built in. Say you settle with Home Basic but a month later want to upgrade to Premium for what ever reason. You can upgrade right through the MS website without having to go to a store and buy an upgrade version. The Anytime Upgrade is also cheaper than buying a retail version.