The Project section link that ToddZ posted is a great way to get the code, but the method where you lift the defrost vent cover is far easier, faster, and requires absolutely no mechanical skills what-so-ever.
You will need a flat screwdriver, and likely need a flashlight.
Gently pry up the defrost vent cover using a flat screwdriver, work it up from one end to the other slowly being carful not to damage the clips. Once you've removed the vent cover, exit the Trac, and stand on the step bars (you may need a higher platform if you're vertically challenged), lean over the windshield, and shine your flashlight into the area of the dash that the vent cover was located... You'll find a small silver box (or white box) with a few numbered labels on it - the door code is the 5 digit number that is printed in larger font (you will likely have to contort yourself into some whacky positions to get your eyes on the code).
Once you've seen the code, try it out a couple of times - if you bought the Trac used, you may want to refer to the owners manual to read up on how to clear the owner-specific door codes (potentially installed by the previous owner), and instal your own code. It's important to note that you cannot delete the factory installed code that is on the control module.
Sorry about the novel - but I hope it of some assistance.