Giroud,

You can't use Windows Media Encoder or even the beta Studio Edition to produce the elementary .vc1 streams that Scenarist requires. Although I read elsewhere (thanks Serge) that you could take a compliant .wmv file and use Windows Media Stream editor to strip out the elementary video data.

Microsoft has a VC-1 encoder especially designed for HD DVD and it's free to studios producing commercial HD DVDs, so it might be worth contacting them about it.