Licensing

[John Doe]

I own two copies of Office. One is Office XP Student and Teacher Edition
for PC, and one is Office v.10 Professional for my Mac. I am selling the PC
and buying another Mac. I wanted to know what I can do?
1) Can I install my Mac version on 2 machines?
2) Failing that, can I sell my Student And Teacher Ed and use the money to
buy another Mac copy?
3) Is there some kind of trade in promo?

Thanks for the Help

Brian