One of the first ways I tested Windows XPs remote desktop feature was by connecting to my desktop with my aged IBM z50 Windows CE device, using a terminal services client from Microsoft.
Even though Ive since ditched Windows CE on the z50 for NetBSD, Ive been able to continue connecting to my XP box using Rdesktop, an open-source Remote Desktop Protocol client. In fact, I wrote this using Microsoft Word through Rdesktop.
The source code for Rdesktop is freely available from www.rdesktop.org and will compile and run on pretty much any Unix-based operating system with X Window System. In addition to the NetBSD z50, Ive run Rdesktop from desktop machines running Red Hat Linux with equal success.