Vista Ultimate was supposed to be the version doing this. Turn UAC off and see what happens. My present experience with Vista Premium has been excellent. No problems at all, even using non signed drivers.
In Vista x64 the only way to disable driver signing enforcement is to hit F8 while booting and choose it (near the bottom of the list). You must do that every boot if you want it disabled. Otherwise unsigned drivers simply don't work.
I always disable UAC. I think I can manage not to open spyware/viruses myself. Not like I've ever gotten either unless I was doing it intentionally to play around.
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