My friend had to convert a machine from vhd to vmdk, i was really suprised that this can be done using the software that i have been using for 2 years 😉
and the winner is : WINIMAGE 🙂
On ntpro.nl it is well documented with screenshots.
http://www.ntpro.nl/blog/archives/194-Convert-Virtual-Disks-from-VHD-to-VMDK.html