It is exactly 1 Remote Desktop Connection you can have at once with XP Pro. What has been mentioned above is connections to shares on the PC.

If it is XP Home, then you can't use M$'s Remote Desktop. With that OS you need either Remote Assistance or 3rd Party Software. Also here you can only have one Connection at a time.

There is an application you can use to create multiple remote desktop connections to an XPPro machine called WinConnect. It allows 3 to 21 simultaneous connections, depending on the licensing you buy.
Although WinConnect works well and is cheaper than a Windows Terminal server, by the time you buy your XPPro license, multiple Winconnect Licenses, and beef up the machine to handle the extra connections, you are approaching the cost of a dedicated basic server to handle your task. The latter might be the better choice.