Unfortunately
the MPC 1000 is one of the few hardware devices where the USB port doesn't negate the need for a separate MIDI interface, so you will definitely need to buy one.
A MIDI to USB cable "is" a MIDI interface, and while inexpensive you kind of get what you pay for, and if you feel you will also need an audio interface I would definitely recommend killing two birds with one stone by getting one that is both an audio and MIDI interface.
What software and kind of computer are you using?