Can I reuse the MS Office license key thats on my MacBookPro?

I'm not sure which version of Office you're using, but for Office 2004 for Mac, there's no activation process on installation. The software does check to make sure the same key isn't being used at the same time, but if you stop using it and install the software on one machine you should then be able to reinstall it on a different machine with no issues.

If you're concerned about legalities, you should know that one legal key can power only one copy of a software. You can install it, and uninstall it unlimited number of times. You can use it in a different PC as long as that key is not powering the other PC any more. The crux is - one key, one PC.

"I found in the past that I had to ring MS Support to activate Office again after say HD crashes, reinstallations etc. The automatic internet activation failed - but after explaining the situation I was issued with the activation code.

If you uninstall it should be no issue whatsoever"

The real problem is how do you deactivate your product key on the mac? Do you completely remove all Microsoft Office related files on your computer? Or do you have to go through a certain uninstaller to deactivate your product key on your computer in order to proceed using?