mcreefer:
Plug this into your pc first and run a few cards through it with a capture program and you will see a pattern. Then once you figure it out, you can snip the end and plug it right into your arduino. From there your on your own. I don't know how the arduino is going to like it.
http://www.ebay.com/itm/USB-Mini-Portable-Magnetic-Stripe-MSR-3TK-3-Track-Swipe-Credit-card-reader-/310423171499?pt=BI_Credit_Card_Terminals&hash=item4846a9b1ab
The device is USB so I don't think snipping the plug off and plugging it into the Arduino will work. You would need a USB host shield https://www.sparkfun.com/products/9947? or try hacking the hardware to intercept the card data before it gets converted to USB, though this really depends on how the hardware is used so probably won't be easy.
Your better off with a card reader that has either RS232 http://circamicro.com/p-1155924-zu-m1242l4dk-card-reader-2-track-swipe-rs232.aspx?currency=GBP or PS/2 http://www.ebay.co.uk/itm/PS2-Magnetic-Stripe-Credit-Card-Reader-3TK-PS-2-/180609077842#vi-content as Arduino can read/write PS/2 http://www.arduino.cc/playground/Main/PS2Keyboard