Anytime Upgrade with 64bit Vista

So, I had 32 bit Vista Home premium, but wanting to move to a 64 bit OS, I
used my schol enrollment to get the 64bit DVD of Vista Business... While it
is installed and working just fine, I really do miss the media center aspect
as I used it daily with my xbox 360.

So basically I want to upgrade to Ultimate. The problem is, when I look at
the Windows Anytime Upgrade Disc that was provided with the Home Premium
(when I bought the computer), it says that it only contains the 32-bit
software. I want to know, if i do the upgrade to Ultimate through MS, will I
be able to download the small file from them (that takes care of license
stuff) and then put in my 64-bit Business DVD to do the trick?

I know that all DVD's contain the same things and that the key (or in my
case the file i download from MS) will unlock the correct features, so
theoretically I can see it working, but I just wanted to make sure... Thanks
everyone for the help...