> Now what do I need to type on the commandline to start these systems ?
For the HP IPC, you need only its ROM -- HP-UX is built in. The command would be "mame hp_ipc".
Floppy images with software are available from HP Museum and other sites (see below). To run the demo, use "mame hp_ipc -flop .../Bundled/IPC_Demos.img" (get the image from coho.org site).
With a bit of effort, you can attach an external hard disk (using the amigo_drive simulator) and install the SDK on it -- I've been planning to write this up somewhere, maybe soon