OK, first you need to make sure that the PC itself is able to connect to the network. It should have a valid IP address in either the 192.168.x.x, 10.x.x.x, or 172.16.x.x - 172.31.x.x ranges.
Secondly, I'm assuming that you've got XP Pro and not XP Home. If you have Pro, then you need to right-click on the My Computer icon, select the Properties choice, and then go to the Remote tab in the dialog window that appears. Remote Assistance isn't necessary, but the Remote Desktop settings need to be set to allow, and you need to select a remote user.
Also, you need to make sure that the user has a password. No password = no connection. At least they got that right!