Swap XP and Vista between 2 machines

[eaw2539]

Hello, basically this is my dilemma: I just purchased a Sony Vaio P with Windows Vista preinstalled and it runs very slow, of course. I have many computers lying around that could handle Vista, but have XP, so I naturally would like to swap the OS's on the two systems. Unfortunately, that Vaio did not come with Windows discs (or a disc drive, for that matter, but I can purchase an external if my plan is viable). I do have a Windows XP SP3 system builder disc, as well as a copy of Windows Vista Home Basic I downloaded from the internet, and I do not know what type of disc it is (although I believe that it is NOT oem). Here are all of the relevant Windows activation keys I own: HP oem XP (I don't know what service pack), Dell oem (again, don't know the service pack) and the Vaio's Sony oem Vista Home Basic SP1. I also have the key that came with the XP system builder disc, but that is on my main PC and I'd like to avoid using it if at all possible, although if it alleviates my pain, i'd do it. It's the Vista install on the XP machines I'm most worried about because of the oem key I'd like to use.

I've done a ton of reading about this online, but it's all so confusing to me, I'd like to have someone knowledgeable about this look at my particular case and tell me if this is doable before I mess up both of my systems (especially since I have no recovery discs for the Vaio).

What I am basically asking is if what I wish to do is possible with what I currently have. If not, I am asking what I need in order to complete the swap. I'd like to keep everything legal and legitimate.

Thanks in advance.

 

[eaw2539]

Update: I've been doing some more reading and I'm pretty sure that I can't do what I'm thinking of. But I am going to college this fall, and if i am eligible for the windows 7 upgrade discount would this work: upgrade the Vaio to 7 (so that it would no longer be oem, then swap it with my main pc (the system builder key). If that would work, what kind of windows 7 disc would I need? The one that I get from the upgrade, or would I have to find a different disc somewhere?

Thanks again.