Windows XP has a limitation on a computer can be only controlled by a local user or a remote user. Pretty troublesome if you want multiple users to login remotely without interrupt the existing user session. Here is a quick hack by Riccardo Raneri to enable an ability login concurrent users through Remote Desktop Connection:
… Very useful, for example, if you’ve a very strong PC and you want your wife/friend/brother to use an old computer like a “terminal” to use applications on the new one, at the same time of you. Other application of the same technique: you’re at work and you want to connect to your home PC, without blocking your wife that is using the same computer to check email…
Windows XP Multiuser Remote Desktop – [Ricky’s Web Review]