Thanks for the replies.
Marc, that's good thinking - I tried getting a site key from XP, then using it in Windows 7 with no luck, but was worth a try (as I don't know much about it either)!
Arro, I'll try those steps in the order you listed to see how it goes. I'm running Windows 7 RC 64 bit, and I wonder if somehow that causes a problem that is not there in the 32 bit version (could explain how some have had success and others haven't?)
I'll let you know if it works out, cheers!
Edit: no luck with this for me so far... it won't generate a site key whatever I do, and I think now I've reached my licence limit through failed attempts. I'll keep trying though