Hi,
  collect old UNIX machines -- I have [...], HP 300,
Do you mean HP 9000/300?  (I presume you don't mean the poorly named
HP 300 Jornada handheld :)
The HP 300 (codename "Amigo") is an exceedingly rare computer from 1978 or so,
and didn't run Unix of any kind.
Pictures at: 
http://www.sieler.com/hp300/  (someone else's)
and 
http://www.sieler.com/hp300_2 (mine)
If you do have an HP 300, boy...do I want to talk to you! :)
thanks,
SS
Stan Sieler                                           sieler(a)allegro.com
www.allegro.com/sieler/wanted/index.html          www.allegro.com/sieler