Well...
Due to rampant pirating M$ now says one cd, one machine. It has to be activated like xp does. But you can get multi user licences for it if you really need to. Gets a bit pricey. But like the guys said you can download open source software that is just as good, in some cases even better. I used Sun Office back when it was still a baby project and was very impressed. I bought the finished product for $60.00USD and have it on so many machines I lost count. I have also used Atlantis Ocean Mind and Abiword. Both totaly free. Goolge around for them and give them a try.