If you care to go to the trouble of getting them upgraded to XP Pro, then Remote Desktop Connection (RDC), which is a part of XP Pro, is a far better choice. Any client with the RDC
client software installed (it's in XP, and free for 98, etc.) can remotely control an
XP Pro machine and it only transmits neccessary mouse and keystrokes, resulting in far better/faster control.
RDC is one-way connection -- from you to the remote host only. It's not interactive and that's why it's faster. You would need to be on the phone with them, explaining things... and then you would be done sooner too.
See here:
MS RDC in XP