Kavie - So you have the same sounds on your computer that you used in your MPC? What you're going to have to do is move the MIDI notes over to the redrum machine's track on the track view. Then, make sure you load the sounds to the corresponding note.
The way I'd recommend using the MPC with reason is by using the MPC as the master controller and reason as a slave. What you want to do is connect the midi out from the MPC to the MIDI in on your computer (assuming you have a midi interface device attached to your computer). Then set the MIDI out to the right settings in the MPC, and set Reason to accept the messages. I would normally be able to go into greater detail but my equipment is on hiatus for the next few days. But if you need help you can hollar the Medicine Man and he'll be able to relay any messages you wanna shoot my way. In fact, ask him for my number if you'd like since you're only out in Oakland. I can have you roll through my pad when I move in sometime next week and show you how I have everything synced up.