XP Pro repair mode – activation needed?

Anyone know if using an already-activated WinXP Pro as a repair disk (when the client’s own disc is not to hand)runs foul of Activation? I.e., if used as you can use a Win2000 CD to rerun Setup to repair an installation without overwriting it – by selecting Repair from the install options – since the serial no. of the ‘new’XP CD doen’t match the already-installed no.,is there an activation problem at the end of setup? Does it look for a serial/activation code based on the original CD installation, or one based on the ‘repair’ CD? Which amounts to saying: is the origibal XP CD any use in repairing other installations, or is this something else closed off by activation issues? Since I haven’t actually done this yet – except on my own system -(and would know the answer if I had), I’m just trying to see what options there may be.