In July, along with the major release 4.1 of vSphere, VMware also updated its physical to virtual (P2V) migration tool vCenter Converter to version 4.2 (build 254483). Just a month later, the company also updated the standalone edition of the tool to version 4.3 (build 292238).

An important information that passed under our radar about these upgrades is that VMware dropped support for Windows NT 4 and Windows 2000, along with support for the OVF format and the VMware Consolidated Backup (VCB) format.

A virtualization.info reader reports that it’s still possible to convert a physical Windows 2000 into a vSphere 4.1 virtual machine by using the old Converter 4.0.1 standalone, despite this scenario is not supported by VMware.
A Support engineer provided the following “workaround” to our reader:

I can only suggest to workaround this by converting to esx 4.0 with converter 4.0.1 and move the VM to the vsphere 4.1 cluster afterward. In that case converting to ESX 4.0 is supported from converter 4.0.1, and vmotion from 4.0 to 4.1 is supported, you only add the vmotion step in the workflow, and need a 4.0 host. I understand it’s not a definite solution, but it might help if you’re stuck at one point.

http://virtualization.info/en/news/2010/10/vmware-drops-support-for-windows-nt-and-2000-in-vcenter-converter.html