iamhives

I have Vista Business x64 installed from a full (non upgrade) disk and running nicely on my main PC. I also have jus received a copy of Ultimate full install licence. I want to replace the Business on my main PC with Ultimate and then reinstall the Business version on a new PC with minimal rework. How do I do this. Can i upgrade the Business using the Ultimate key and then reinstall the Business and use the key previously on my main PC with the previous Business install (I assume I'd have o call MS to reactivate)???