I own an iPaq rz1710 running Windows Mobile 2003 Second Edition and I have been syncing it to Outlook data on Win XP for several years now. Before that, in the Win2k days, I had Win CE devices that I synced up. With Vista I couldn't get the Outlook data to sync up...at first. After fighting with it for a while, I finally figured it out.
A few basics: ActiveSync on the desktop has been replaced by "Windows mobile Device Center" (WMDC), while ActiveSync remains on the handheld. Your Vista machine may already have WMDC, but there is a critical upgrade you need to get from Microsoft (easily found if you search on WMDC). Whether you're installing WMDC or upgrading it, have your handheld connected by USB (or whatever you use) during the upgrade.
After getting WMDC upgraded, my desktop and handheld formed a parternership right away, but the Outlook data was not coming over. I may be a special freak case because I maintain multiple .pst files. My main .pst file actually resides on a jump drive, while the .pst that resides in the conventional location on the C: drive is just an empty shell. I noticed that when I added a new contact on the handheld and then sync'd up, the new contact did show up on my desktop Outlook, but in the C: drive .pst file. That's because Outlook regards the C: location of the .pst as primary and anything else secondary.
So I fixed it by (1) setting the jump drive .pst file as the primary; that wasn't enough to fix it so I also had to (2) delete the reference to the C: drive .pst file from Outlook. Microsoft has you do (1) in a funny way. You go to outlook, tools menu, email accounts, view or change existing accounts, then select the preferred .pst file from the dropdown titled "Deliver new email to the following location". Step (2) is done by navigating: Tools -> Options -> Mail Setup -> Data Files, select .pst file to remove reference to, and click Remove.
After that I had to shut down WMDC and Outlook, then restart WMDC. Now, when I pressed sync, I saw the little bugger go to work and download all my Outlook contacts, calendar items, notes and tasks to the handheld.
One other annoying thing about the Vista approach to handhelds is that the client software is really split between two areas, the "Sync Center" of the Control Panel, and WMDC itself. A lot of tasks seem to start in the Sync Center, but the real work (such as selecting what items you want sync'd up) is done in WMDC. Microsoft makes it hard for you to launch WMDC from the Sync Center, but here's the secret: go to View Sync Partnerships, then double click on your device.