same thing. One is just a more consumer-ish face to the same technology: The remote desktop protocol, RDP.
On XP pro you are looking at a simple remote access program that has no management features and only allwos one user to access the workstation remotely at a time. ther are exceptions, but more the most part that is the case.
On a windows server (2000, 2003) you can a whole suite of management and accessibly features with it. For example ,some of the additonal features include multiple user logons, using terminal services to replace pc terminals with 'dumb terminals' that rely competely on terminal services for everything (no HDD; just flash memory, ram, and a NIC), load balancing of this traffic, remote control sessions, logging, and much more.
Terminal services is more of an enterprise implementation of the same technology. It is geared more for enterprise remote access and has all of the security and management features that enterprise clients require....