I've been running various builds of Windows Mobile Device Center for awhile now. For those of you who don't know its basically the replacement for ActiveSync which controls partnerships for Windows Mobile devices under Windows XP. Well for Windows Vista the mobile devices team has completely re-written this as a new application. Essential it manages the partnership with your Windows Mobile 2003 or 5.0 device. There have been many improvements in synchronization, setup, photo management, media management, file browsing and as you can see the user interface is much more streamlined.
I've used many versions of ActiveSync in the past an Windows Mobile Device Center just works and is really simple to use. I guess that's what you need when syncing mobile devices anyway!
So check out the download at the Windows Mobile Device Center's webpage. They have all the system requirements there.