If you want to try, this sequence worked for me:
- shutdown the VM in XenServer
- Export it somewhere so you can work on the VHD Virtual Hard Disk File (I have build an NFS Virtual OpenFiler on the new server and connected to both virtualization server)
- with the aid of http://www.winimage.com/
Professional, under "Disk" you can find "Convert Virtual Hard Disk Image"
- convert to VMDK