Without claiming to know for sure, but based on what I've managed to find out from the four corners of the WWW, I reckon you need to activate Vista before DRM will function properly. Most Vista users will never encounter this same problem since by far the bulk of Vista sales are pre-installed and pre-activated. That's why I think it's an activation issue. AS with XP, Vista is 'hard coded' to run in 'reduced functionality' mode after a set amount of time, until it's successfully activated.
Which leads to me another, possibly related issue. Since you haven't yet activated Vista I'm assuming it's a self-installed copy on a PC you already own. I do know that Vista has very exacting requirements regarding the video-card, sound-card and several other system components. If any of these do not meet Microsoft's own criteria for being wholly 'vista compatible' (by their definition of the term) you will have problems with the playback of DRM-protected content.
Edited by pip22, 26 November 2007 - 10:23 AM.