To copy profiles from one machine to another machine on a domain and have it so XP carries on using those profiles on the new machine instead of it creating a new profile like jdoe.DOMAINNAME. Extract the key below from the registry of the old machine
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\Current Version\ProfileList
Copy the profiles over to the new machine.
Once copied you may need to set the permission up again on their profile folder. You may need to add the user back in and give them full control.