The "Corporate" version you guys keep referring to is a version of XP Professional. Microsoft calls it XP Workstation and it can be installed across the entire office depending on how many licenses you purchase with it.
The licensing as I understand it for the Workstation version starts in at 10 and goes to whatever you need. This is what I gathered from the launch "party" I attended last Thursday here in Birmingham and asked the MS Rep about it point blank since I deal with some small customers that want to move to XP in the next year.
Since most all middle to large corporate customers tend to make OS upgrades when they buy there new systems every couple of years. Then they buy Compaq, Dell, IBM and Gateway; so they will not have to "activate" the OS since it will have already been loaded on the system ahead of time.