I think that 3 computer thing is right. I was reading something yesterday or day before about Apple's iLife08 and how it has Numbers in it now (to rival excel), and the article mentioned that the student Office for Mac is the best selling non apple software for Macintosh computers, and said you could install it on 3 computers. I don't have the link anymore or I'd put it here.
Does this work on Office Professional then? I got a free copy of that for going to the MS Launch Event for Vista and Office, but I've been real reluctant to install it because I thought there might be some hassle if I switched computers it was on a few months later.