In corporate environments, you should be able to get such numbers with some investigation. Sometimes, they're put on the machine itself for auditing purposes. If your work machine is registry-enabled, but REGEXP32 and surf around a bit on a few hits which google should get you started with.
Of course, previous versions of Office are for sale fairly cheap on craisglist and in computer shows. You might also try getting a friend in college to buy you a current copy for the student price, which is very cheap.