The fastest way to see MP would be to fly from Lima to Cuzco. There are flights on Lan airlines and Star Peru. Then you take a train from Cuzco to Aguas Calientes. From AC you take about a 20 min bus ride to MP. AC is a VERY tiny town, not much there for tourist. Just some restaurants, and I think a hostel. I don't even know if there is a hotel. It is basically the on/off point from the train to the bus. Let me see if I can find out how long the train from Cuzco to AC is. I'll work on that.
I don't know if you have to sign up for a tour from AC to MP, or if you can just hop on the bus independently. I would definately suggest taking a tour of MP. It is huge, and you'd basically have no idea what you are looking at. Lil' Lori