HP sells the SuSE Enterprise CD right now (ver 7.0) for $600...uninstalled. (Admittedly, that's the way I'd prefer every OS from the manufacturer.) I don't think HP's "certify" comment is a very strong endorsement -- I think they certify lots of things, like Banyan Vines and Netware 4, but that just means that they've determined that drivers work for it.
Is it significant that Dell didn't join the annoucement?