I did something similar using my RM1x.
There's probably more than one way to do this, but the simplest method would be initially to work out exactly how long your song is in bars and set that in to your sequence. Then create a program with your chosen samples in and record your sequence, hitting the pads with your samples on at the times you require.
That's not the only way, as I said, but it will probably pay you to spend some time learing the MPC before trying different things out. You could create a MIDI file offline and transfer it over, as long as you make sure that the samples in the program have been assigned to the right note numbers.
Of course, doing this means that you and your band are tied to the sequence length and if you wanted to ad lib, you'd come unstuck. The trick is to create a sequence and song length appropiate enough to make it look totally live and spontaneous
It's a trick people like Robbie Williams use to great effect. His entire live show runs on top of a heavily sequenced backing provided by two Akai S6000 samplers. They program all the strings, brass, samples, loops and pecussion and save them all as .mid files. The S6000's MIDI playback device is then used in conjunction with the SET LIST feature and the drummer controls the whole lot. If you watch any Robbie Williams live show, look to the left of the drummer and by his Hi Hat, you'll see 2x S6000 control panels. In actual fact, the SET LIST feature on the S6000 was designed by Akai in conjunction with Robbie's keyboard tech.
As I said earlier, I used to use my RM1x to sequence up stuff like strings and brass, then play back to a click track. I have just got an MPC1000 and I am now looking at hooking up my MPC500 to my Yamaha DTXpress drum kit to investigate the possibilities there
Hope that goes some way to helping
