About once a month I decide to fight this again. Occassionally the Treo and WMD decide to talk and sync, then nothing. What I have:

Vista Biz 32-bit
WMD 6.1
Treo 750; current inso far as I know

Gave up on BT, just trying to get USB going. When I plug in, the Treo shows it going through the steps, stopping at the Active Sync screen. I think I see a dialog flash "disconnect", but it's too fast to catch. It says I'm connected, but the WMD display shows the Treo but says it is not connected. When I tap "Sync" on the Treo, nothing happens. Last sync was a month ago, but the display now says that I am up to date.