Most corporate version to not require activation.
The way this works is when XP is installed it creates a hardware ID this number. This number is created by these parts: Serial number of system volume; NIC MAC address; CDROM; graphics adapter; CPU; hard drive; SCSI adapter; IDE controller; processor model; RAM size. There's also a check to see if the hardware is dockable or not. Then its transmits this long number during activation to MS. Which transmits back at confirmation code if it has not been activated before(that license key) If its has been activated before MS servers will compare the codes to see if they are identical, if they are slightly different it will be ok with it and confirm the activation. If they are very different it will decline activation. And every so often the activation program checks the computer to make sure it lines up with the machine ID. If it is slightly different it transmits the new machine ID to the servers. If it is very different it will require activation again. To get it to activate again you just phone them up tell them what you changed, then they give you the story of how they don't like doing this but will do it this once.(don't have them do it to many times or they won't do it) So thats how activation works.

Man am I glad we use a cooperate license at work.