You already know that a new version of the Windows Mobile Device Center (WMDC) Beta has been released for Windows Vista RC1; its build number is 6.0.6526. WMDC Beta 3 enables you to setup new partnerships, synchronize content and manage music, pictures and video with any Windows Mobile 2003- or Windows Mobile 5-powered device.
The Windows Mobile Device Center Beta is currently available as a stand-alone installation here. In a few weeks it will be available through Windows Update.
Although formal support is not offered for this Beta release, you're encouraged to use newsgroups to help answer your questions. The Windows Mobile also welcome your feedback at firstname.lastname@example.org.