Installation of Vista with OEM disc

I am upgrading my Ram and Hard drive; my ram was successfully upgraded and now i am installing vista on my new hard drive which was successfully installed in the T400. I was told that Windows vista installation discs had all versions of vista on them and that it only depended on the key that came with your computer. I have an OEM disc that came with my old xps m1330, and i was wondering how i get it to work. More specifically, when i boot to the disc it doesnt give me any options to pick what OS i want or even to put in the key. Am i doing something wrong, or have i made a mistake somewhere?
While the disc is clearly labelled Windows Vista Home Premium 32-Bit, i was under the impression (as stated above) that it did not matter. If i can't do it with this disc, is there any way to downgrade windows?

-kent

 

First, note the 32-bit oem dvds do not have the 64-bit version on it. The 64-bit will typically have both.

Now, If it is a standard oem disk (and with Dells that is never certain), punching in your key will tell the install routine what version you have.

Or, you can proceed without entering a cd-key and Windows will warn you that you can go on after picking your version, but you must add your key later.