I installed Win8 Pro Upgrade last night. I tried to install XP so that I would have a fully activated OS already on the drive to upgrade from but for some reason I couldn't get XP to install on this new 1TB drive. I ended up just putting in the Win8 DVD and installing it (I was curious if it would work) but of course it won't activate.

I think I know why XP didn't install so I might try again tonight.
OR since I already have Win8 Pro installed should I just try the double install thing?

Are there any technical reasons not to do it this way?