The switches use one of the output pins from your parallel DB25. If your driver board has terminials available that gives you access to the pins, it's fairly easy. The Xylotex site has some simple layout schematics for wiring your switches in either parallel or series configerations. You'll need resistors to pull the circuit low and then tell your software your setup so if recognizes when the circuit goes high (or visa versa), so it will stop (if a limit) or reference (if a homeing switch). Or, both if your software is capable.
As far as switches, just some small microswitches will work fine. The kind with a small arm that bumps the switch. Wire in normally closed (NC) so that when a switch opens or a wire breaks, your circuit will make note of the open circuit and stop things.
Do a search for breakout boards... they make things much easier and will protect your computer and provide the necessary resistors onthe board.
Take a look here for info too...
http://www.campbelldesigns.com/breakout_board_plus.htm
and
http://www.pmdx.com/
-marc