Make sure you use 16 bit video, or the default X configuration won't run under VPC.

Also,  for those who have asked about Virtual PC,  info can be found  @ http://www.microsoft.com/windowsxp/virtualpc

I was using VMware since it's inception, but recently switched to VPC,  Both products offer simular capabilities.

Something else of interest may be the new Virtual Server, a real solid build was just released (321),  follow the links from here and join the beta @ http://www.microsoft.com/windowsserver2003/evaluation/trial/virtualserver.mspx and give it a try.