Vista Home basic is just windows. No Aero, no DVD decoder, no media center app... But, I understand that you can do some sort of registry hack to enable Aero, but it's definately not supported.
Vista Home Premium adds the Media Center application, which is really nice if you throw in a TV tuner card in the PC. It also has Aero and the DVD decoder.
Business doesn't come with a DVD decoder (but you can get a 3rd party decoder from nVidia for $20 to $50), nor does it have the media center app, but it does have Aero, all the business conectivity and advanced networking, Remote Desktop, a better backup system, shadow copy, and Previous Versions. Previous versions allows you to revert files to earlier revisions just by right clicking on them. Great for recovering files that you accidently saved over.
Ultimate is a combination of Home Premium and Business, containing all the features of both plus a few extras like Dremescene (Animated desktop) and Bit Blocker and the retail version comes with both 32 and 64 bit disks.
All retail versions of Vista can be installed as 32 or 64 bit flavors with the same CD key, but you must obtain the 64bit media from MS(for shipping and handling only), or elsewhere on all version but Ultimate.
Retail upgrade versions for all are (from newegg):
Vista Home Basic. $97
Home Premium $145
Business $150
Ultimate $250
I have 4 PC's in my house hold so I went
My primare desktop/gaming rig: Ultimate
My Media Center: Ultimate
My Laptop is running home premium
The PC I gave my Dad is running home premium
That said, I have just purchased a copy of Vista Business for $99 from the CompUSA that is closing near me for my laptop.