I have one of these, working hard as a fine samba and 
netatalk server running 1.6k (http://www.caseydoodle.com/netbsd6.png) .
To set up serial console:(at SRM prompt)
>>>set console serial (after reboot console is serial)
My box uses graphics mode- XFree86-4.2.1 and runs very well. This is a
21164 CPU machine. The box has a built in vga chip. Get docs from hp
website.
Best -Mel