need help with recording through midi

i got the keyboard hooked up and i want to record a melody through midi on a pad..how would i do that?

I'd sequence it into a MD recorder or whatever recording media you have, and sample it.

If my understanding of your question serves me correctly, you just change the drum setting(defaulted to drum 1) to midi. Depending on the type of keyboard you are using, set the midi device number(1a, 2a, 3a etc.) to match the track number/midi channel on the keyboard. All of this is ofcourse pending you have all of the proper midi connections...If you are already able to hear the sounds of your keyboard via the midi setup, recording is simple. Just like recording with samples/internal mpc sounds, you set the tempo and time sig. if necessary and hit record and play to set mpc into record mode. If I have misunderstood the question please give more info, but this basic setup should get you started in the right direction...
Recording this way won't allow you to control the parameters of the melody you play from the mixer settings of the mpc, but you can control the on/off (mute) function of info on that track..