The following interefaces are supported:
- USB (+5V, ground, D+ and D-)
- PS/2 keyboard 'wedge' (goes between keyboard and computer, inserts keypresses)
- RS-232 (+-10V serial)
- IBM 46xx (for point of sale computers, rare for other uses)
For our use, we like USB the most because its the most flexible. However, you may want to use these for an embedded project - say where it connects directly to an AVR/PIC/ARM or whatever, you'll probably want to go with the RS232 interface for the ultra simplicity or PS/2 if you don't mind a little extra parsing
You'll need two things to change the interface, one is the proper cable (you can make your own but its a real pain, you'll probably want to just buy it) and a power supply if necessary. RS-232 requires a power supply, but the others do not.
This is the USB cable, for example: