Just came across the following post, How to create a XPe guest on ESX, I have got to say well done to
http://collegegeek.org/2008/07/11/xpe-on-esx-3x/
It may be easier to read the above after reading Zach other post on running XPe as a guest, this time on Workstation.
http://collegegeek.org/2008/06/17/using-vmware-to-build-and-run-xp-embedded/
Again well done of a couple of excellent posts.