Try here first:
http://www.ultimarc.com/ipac2.html
Right, see the diagram about halfway down the page for buttons. The GND or Common terminal of the button switches all go the the I-PAC GND and each NO (Normally open) terminal goes the the corresponding I-PAC terminal (NO terminal of Button 1 for Player 1 goes to "1 BT 1" etc.)
The joysticks will have 4 microswitches on the bottom that connect in the same manner to the I-PAC terminals labelled UP, Down, Right, and Left.
One commonly overlooked point: When you move the joystick handle upward, the joystick actuator closes the LOWER microswitch, so the UP microswitch is physically the lower switch on your CP.
Also, you want to use either .187 (3/16") preferably, or 1/4-inch quick disconnects to connect the wires to the switches.
I like 22-gauge stranded wire, but some people prefer solid, that's a whole nother debate.