Microsoft Remore desktop is free and available on the XP home cd and Pro.
Copied from:
http://www.microsoft.com/windowsxp/downloads/tools/rdclientdl.mspx
"Note The Remote Desktop Connection software is pre-installed with Windows
XP. To run it, click Start, click All Programs, click Accessories, click
Communications, and then click Remote Desktop Connection. This software
package can also be found on the Windows XP Professional and Windows XP Home
Edition product CDs and can be installed on any supported Windows platform.
To install from the CD, insert the disc into the target machine's CD-ROM
drive, select Perform Additional Tasks, and then click Install Remote Desktop
Connection."
There is also an install file available for free for 0lder Windows versions.