VM migration from VDS to VSS is pretty easy via the Migration Wizard (available in both the vSphere Client and vSphere Web Client):
Migrating other interfaces from the VDS to a VSS is not quite as straightforward, but if you want to go from one type of distributed switch (like the 1000v) to a regular VDS, that can be done entirely from the vSphere client. Select the VDS in the networking view, and click "Manage Hosts". That wizard there will let you migrate pNICs, vmkernel interfaces, and VM networking. I know that isn't what you asked for, but based on some of your other posts, I thought that might be relevant info. 