The light fixture is this one:
Chrome Finish Duotrack 5 Light Marte Kit
I'm not sure the voltage of the fixture, but the specs on Home Depot's site says "This kit comes complete with all required mounting hardware and five 20 watt 12 volt MR16 halogen bulbs." Does that answer your question?
As for the dimmer switch, it's a basic Levitron one, probably a standard incandescent one. So are you saying the problem is the dimmer switch, and that there's a specific switch I can get that will work well with the hallogens? If so, that's great news. Can you suggest which dimmer switch?