midi out from your keyboard into...
midi in on the MPC...
midi out on the MPC into...
midi in on your keyboard...
Check both manuals for the proper internal midi configuration for each unit, if need be.
Your keyboard will trigger (play across the keyboard) the sounds you load/sample into your MPC, as well as its' own internal sounds...
The MPC's sequencer will control not only sounds from your MPC, but also the sounds from your keyboard.
Your MPC will handle all the looping of whatever you sequence - should be on/around page 28-ish...
Check pages 26-30 in the manual
(well, at least the manual for the 2000xl. I imagine the functions are hella similar, but the 2000 manual is hard to find online - well, ok, it's all but impossible. Akai doesn't offer it up anymore for some reason...)
You can go here too for MPC help, but just like the home rec. BBS, they don't take kindly to people asking questions that are clearly outlined/answered in the manual...
http://www.mpc-forums.com/
Check here, too (old page, but many of the links are still active:
http://www.synthzone.com/akai.htm
and here for the manual if you can't seem to find yours...
http://www.vintagesynth.org/akai/mpc2000.shtml
By the way, page 11 has a diagram showing how to hook your shit up correctly...
good luck.