retail Home Premium 32-bit to Ultimate 32-bit to Ultimate 64-bit.

Got a older computer, has windows vista on it (32bit)

Vista is a retail Home Premium copy, that was installed, activated, and used
since nearly a week after it was available, about 3 months down the road is
was upgraded over the internet via MS's upgrade system to Ultimate.

Now heres the dilema...

This machine is getting the boot, being stripped down and parted out.... a
New machine is ready to roll, so basically everything is going to be GONE. A
fresh install of windows is needed..

the Question arises, being retail, i don't think switching to a new machine
is going to be a problem at all, BUT

Should i be able to install windows Vista Ultimate STRAIGHT AWAY onto the
machine, or does the upgrade process have to be done (and how so?)... also,
being 32bit version, and then upgraded to ultimate (retail).... i'm not sure,
but would installing 64bit version of ultimate cause any greif? Is it
possible? (as we've got a 64bit DVD here already....)

anyone got any ideas?
Thanks.