I had some trouble creating xp images directly on vmware ESX sever earlier. I had to find the right disk driver and configure vmware virtual HD in a certain way to install windows XP.
I tried vmware converter.
Turned out it is much easier to create a xp image using vmware workstation and move it to ESX server. I assume the same will work with vmware server. Since this method worked so well for me, I won even bother you with how to install xp directly on ESX. If you would like to know, let me know and I would be happy to share what I found.