able to run.  The perfect examples are ts10, simh, and
hercules.  The first 
I agree that one might need to emulate the PDP-10, because of its relative
rarity.  As far as IBM Mainframes, one could pick up a P/390E and put it
in a PC or RS/6000 to get a real IBM mainframe.  (Or you could be me, and
go get a 9672 G5)
Peace...  Sridhar