There's a nice
patch for WindowsXP Pro SP3 to enable concurrent RDP sessions. For your (and my) convenience,
here are the files again:
$ ls -lgo termsrv.*
-rwxr--r-- 1 295424 2010-08-26 15:47 termsrv.dll
-rwxr--r-- 1 295424 2008-04-13 17:12 termsrv.bk1
$ md5sum termsrv.*
56f4867bae6fd78e5365a3a7afa59c82 termsrv.dll
ff3477c03be7201c294c35f684b3479f termsrv.bk1
After patching
termsrv.dll (and backing up the original, and escaping
Windows File Protection), we still have to add a new registry key:
HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\Licensing Core\
EnableConcurrentSessions=1 (DWORD)
Reboot, and we should be done.