All Microsoft volume product keys (that are those which are used in companies) should work for Windows AND Mac!

So, the company will buy their seats licenses and the workers could decide on which platform they want to work. At the current state, each Mac replacing a PC would add additional costs...

So the only hope breaking the Office monopoly is either a revolutionary product (which Sun StarOffice/OpenOffice isn't) or the M$ new licensing scheme (the last one seems to begin to make people thinking).