paula

I buy a new computer with Vista Ultimate on it.
My old computer is a dual boot with XP Pro and a boxed retail version of
Vista Ultimate on a second hard drive.
I also have a laptop with Vista Home Premium.
Since my new computer has Ultimate on it can I take the Ultimate off the old
computer and install it on the laptop which is currently running Home
Premium? If so, how would I go about doing that? Would I have to call
Microsoft since the key has already been installed on the old computer?
Would they let me do that?
TIA
Paula