The only thing I can think of is to install Cygwin & setup an ssh server on your XP machine. Then you can ssh into Windows from your Linux box and start the VNC service on the command-line using the ...
I have a mandrake 9 box I just set up that I want to be able to VNC into from my other machines. My other 2 boxes are running XP and already have VNC working fine between them. The windows boxen can ...