You are so right, the existence of HP Linux had totally slipped my mind.  If I 
remember, it is some sort of debian distro.  Am I right about this?  Anyways, 
I remember playing around with it long ago.  I don't think it is yet upto a 
full release.  I think it is somewhere in the 0.9?.?? area of development.  
So, you could run linux on an HP so long as you get an appropiate model.

However, I probably would not go this route as HP-UX is a wonderful OS to run.
 Besides, the point is to learn about HP-UX, not about debian.

--Lance