I've run the Warrior Dash twice, and I plan on running it again next year. Definitely build up your stamina with running and cardio. I get that in usually by "running" on an elliptical machine to spare my knees, but there is a difference between running on a machine and terrain running. Be prepared to dodge trees and jump over logs while running, and if it rained the day before the race you may be running in a few inches of mud at times. Also, be prepared for running uphill, depending on where the race is located.
Don't neglect the upper body with training either, as some of the obstacles involve climbing. All that aside, the Warrior Dash is a really fun event and I think you will have a great time. I have plenty of pics from the two I ran in my album on here.