I have Bryce 6.1 running on Vista Ultimate and the only problem I seem to have is the same old blacked out import of meshes that seems to be a 6.1 specific phenomenon,( they import with all materials into 5.0 without problems). So far, other that that, Bryce 6.1 is ok with Vista.

As far as finding Vista in your neck of the woods goes, I'm sure any computer store that sells computers and software would have it...the manual might be questionable, though, very few software manuals are provide in print form much anymore but instead come in PDF format on the disk..