One licence on 2 OS?

[rendez2k]

I am shortly going to be installing Vista Ultimate on my system alongside XP for testing reasons, and I'm wondering if my ESS licence covers me per machine or per OS? Many thanks.

[s4u]

depends on your license. but usually only one machine

[rendez2k]

Well, I've only got the basic 1 machine licence. But thats my point - in theory it is only one machine or does each OS constitute as a separate machine?

[ASpace]

Your license is per machine (no matter how many Windowses you run on it) . What is 100% sure is that you can't run more than one Windows OS at a time (except from virtual machines but that is another story)