I've used the legit student/full version of Office:Mac 2004 for years, and it can be installed to as many machines as you like, but it will lock you out if another Mac is running it (same serial) and online at the same time. No activation or any other hassles though.

Office 2011 is finally OK, Office 2008 was the biggest, slowest piece of crap I've used from Microsoft (yeah, I had Vista Ultimate for a little while too!).