It may be fixed by now (haven't checked in quite a while), but the most annoying thing ever is that office isn't compatible with spaces - to the point that I tear my hear out every time I try to use word. What happens is that if you happen to switch spaces, then want to get word back, it takes about 2 minutes of random application switching and space switching before word will actually display (instead of thinking that you asked it to hide itself when you clicked on it).
Apart from that, its going to be much cheaper and easier to get office for mac, rather than an xp license, fusion, and office 2007. No real advantage of having the 2007 version either unless you want to be doing some scripting.