Sometimes it seems like releasing software is more complicated than developing it. We really wanted to have this at WinHEC, but that just wasn't going to happen. Fortunately I have an amazing team to help push through all the problems and process imposed upon us. So we have a beta release.
If you're already signed up for the Windows Driver Kit beta then you should have email telling you that the UMDF beta is available. The mail helpfully fails to tell you where to get the beta - it's on the download page for the WDK beta.
If you aren't signed up but you've read this far you clearly want to. Go ahead and do it. Unless you're chicken* that is (or don't have the bandwidth to download a 2+ GB kit).
I really want to write some more about using it, but my team is trying to lockdown for the Vista RC and I don't have time today. In the next few days i'll walk through the steps of installing it, compiling the samples and getting the resulting driver installed.
Until then, the readme file is your friend.
* they say goading can be an effective motivator. Let's try it now.