This is an update to my previous post on this topic.

Windows Vista RC1 doesn't currently have a version of Windows Mobile Device Center (WMDC) for download.

I have however heard that a version is in the pipeline and will be made available around the time RC1 is released to the public. The same thing happened with Beta 2, the testers had to wait a couple of weeks until public availability for WMDC to be made available over Windows Update.