It all depends on whether or not you have a TRUE OEM disc or a manufacturer's disc.
A TRUE OEM disc is defined as the DVD's with the holographic designs with the word "Genuine and Microsoft" on the edges. These disc contains all versions of Vista in that bit version (i.e, 32-bit or 64-bit). It is the product key that determine what version of Vista the disc will install. In fact, if you do not enter a key and continue you get to choose which version to install (i.e, Home Basic, Home Premium, Business, & Ultimate)
On the other hand if you have a Manufacturer's disc, i.e, Toshiba it only lets you install the version that they sold you and it usually includes drivers for your particular machine.
Also, if you have a valid Vista key for a 32-bit version you can use that same key for a vista x64 disc. (i,e. Vista Business 32-bit keys work for Vista Business 64-bit and vice versa)
So long story short...A true OEM version gives you ALL flavors of Vista it's the key that determines what you get...Edited by playboysmoov - 5/18/08 at 1:44pm