Yes, you can certainly use a MIDI keyboard, so long as you have a MIDI input to your computer. (If you haven't, don't worry - you can change the soundcard.)
I don't know what you mean by `comps,' though?
Are you using the MMV in stand-alone mode or running under something else?
Let us know what you're running and I or someone here will get you set up.
Playing a Mg Modular polyphonically is an experience not to be missed.