Swapping Vista Premium and Ultimate

I have two DVDs for Vista, one Home Premium and the other Ultimate.  Both were
purchased, they did not come pre-installed.
I installed Vista Ultimate on my Toshiba laptop, where it works quite well, and
held the Premium version aside until I was done building my latest desktop. 
Long story short, the desktop finished with better components than I had
originally planned on using, and now I realize I could make better use of the
graphics capabilities of Ultimate on the desktop (I use WindowBlinds on the
desktop, and they have some nice Dreamscape images I'd like to use, which my
Toshiba's graphics card won't support).

So the questions are:


How difficult will it be to switch the two versions?  Am I looking at a full
reinstall x2?
Do you think Microsoft will permit me to downgrade the laptop from Ultimate to
Premium without a major hassle? Ideas, opinions, suggestions?  Any are welcome
and appreciated.

1. Yes you'll have to full reinstall both copies (though I think there is a way
to upgrade a copy to ultimate) you could try file and transfer wizard also

2. I think there is a clause in the licensing that lets you install it on
another machine if you remove from your current one, you'll probably want to
double check that one.

Until a few more Ultimate Extras are released, there is no differences in the
graphics capabilities of Premium and Ultimate.

Thanks, that pretty much confirms what I suspected.

And Electronic Punk, I agree and normally wouldn't care which version was where.
 But I'm hoping to sell the laptop and would prefer to keep the Ultimate
version.  It's Aero capabilities are wasted on the laptop anyway.

Thanks for the replies.

I used to install a couple of OS of the same verion and brand for testing
purposes, but I have not been able to do so with Vista. When I installed in one
partition, the present partition was disabled. It was not a boot problem, as I
have several partiton managers and they work with Vista. I gave up on keeping
more than one installations during the beta. I would not be surprised if present
software allows it.