Win XP remote desktop…permissions

I have a customer who would like to remote into a PC in his office from a laptop out in the field. He would be using a broadband internet connection. The twist is that he would like the user of the laptop to only have access to one particular program on the local network, not full control of the PC being remotely accessed. The network is using Win NT 4.0 on the server and Win XP pro on the workstations. The laptop would have the same loaded on it. I am wondering if I will need to sell him some software to do the job he wants or can I just make a restricted user name for the login on Windows Remote Desktop? Any suggestions appreciated. Thanks in advance.