I see from my searches that people seem to be running this emulator / system combination just fine but they don't really go into detail about it.
Things I have learned:
1. You'll need to have the intellivision bios files - exec.bin and grom.bin either in a zip file in the bios dir or as files in a "intv" subdirectory
2. You'll need to have the games in a .rom or .int format
3. You'll need to configure the software directory for the Intellivision component of MESS to point to the roms (defaults to the mess\software dir)
4. It still won't work
5. There are better, dedicated emulators out there (and I've already had them running fine - thanks Nostalgia) but MESS allows you to configure controls for individual games. This feature would be very, very useful for the Intellivision which, for most games only uses a few buttons on the pad, but different ones for different games!
Here's the command line:
\mess0130b\mess.exe intv -cart "software\romname.int"
That command line works perfectly for the colecovision and atari 7600 instances but the intellivision gives me "can't recognize the RAM option 0". AFAIK there are no options to set RAM for the Intellivision in MESS and I'm out of ideas.
Any thoughts?
[Edit]
I simply moved to a new version of MESS 0.131 and everything worked. I haven't seen any reports of 0.128 having problems but they do move quickly on the new version so perhaps no-one had a chance to find out.
I now have Atari 5200, 7800, Colecovision and the Intellivision running well under MESS. Not as much success with the Vectrex emulation, though - the vector rendering in 0.131 makes games unplayable (can't see bullets in Fortress of Narzod, kind of important). Going back to the older version until I can come up with a workaround - I understand the issue is with the MAME vector games too...
Mind you, it turns out my memory was faulty, you can't configure individual games' controls with MESS, only the system. So it was all just a proof of concept in the end. That's the hobby of emulation in a nutshell, really :-)