They might have a point if millions of people were going to rush out and buy Vista. But thats not going to happen, so the Green Party is sadly talking junk.
Far and away the vast majority of PC users will be sticking with their current XP install until they buy a new PC, which will come pre-loaded with Vista. And even then, people don't tend to throw away their old PCs if they still work. They tend to keep it around as a second machine, or pass it on to a relative (instant recycling).
I hate DRM , but come on, Thousand of people dumping perfectly good hardware so they can watch HD-DVD movies? I don't think so