Upgrade versions of software are add ons to the original licence. Means you're not permitted to install the original software on one machine, apply a legally-purchased upgrade, then install and use the original software on another machine.
However, your use of the original software on the second machine is intended as a work around, right? You own a legal copy of an OS but can't install it and use it as a springboard into the upgrade. Personally, I don't see a problem. But to avoid confusion, activate only after the Windows 7 Home premium is installed.
I'm not saying this usage is strictly legal, though, but I doubt MS would have an issue with it. So long as you wind up with a legally purchased set of O/Ss for each computer you're running. "Set" means original O/S plus upgrade per machine.
Edited by Myrkr, 23 April 2011 - 09:40 AM.