Hey Vash: I can throw my two cents in. I lived in Urubamba for two years which is where the trains leave to MP. Start drinking coca tea (even at the airport) the minute you get there, most people get a serious headache for the first couple of hours from the elevation. You want to spend at least 2 days acclimating (cusco / Urubamba) before you make the trek. Trust me you'll be glad you did. Not so sure about people's comments about the 4 day trek being easy, the first day yes, but the start of the 2nd day you hit the stairway to heaven which looks like its going strait up!
I went last minute with a heavy pack and just about stroked out
the morning of the 4th day you come upon (looking down) from 9000 to 6000 feet or so to MP and it all becomes worth it. the town itself Aguas Calientes is a nasty little pit.
Try to see (before or after) the town of Ollantaytambo a cab ride south of Urubamba. They have other ruins quite impressive and the town is very cool. The other direction, you can hit the outdoor market in Pisac great Quechua clothes and stuff.
let me know if you have any questions, still have friends down there, one (Riccardo) in Urubamba owns a great restaurant called Tres Keros - I'll let him know you're coming