At 1500 miles the front end was in need of alignment and the outside edge of the front tires were wearing down excessively.We took to the dealer and they aligned it When I went to rotate the tires at 5500 miles they were worn so bad that I didn't want to put the rear tires (which still looked brand new) on the front. I took the car to Sears they told us the front end was way out of alignment so we had them align it and rotate the tires on 9/13/08.Today I looked at the front tires and they are showing signs of wearing on the outside edge. What can be happening?

Did you ever see the statements in the tire dealer shops stating a specific tire model will last approx. 50-75,000 miles/
This will never happen unless you have your tires rotated every 7500 miles, the front tires wear excessively compared to the rear tires in 90% of the cars/trucks.
Why? Because the front tires in most cases are the drive tires(front wheel drive) causing the front tires to ocasionally spin causing excessive wear and also the front tires are the ones that guide your vehicle down the road, when you turn the steering wheel you are turning the front tires to make the car go in the direction you want thus causing more excessive wear to the front tires, in order to get even wear from front to back tires one must move the front tires to the back tires at 7500 mile intervals, making sure the tires only get rotated to the same side of the car each and every time, if you move a right rear tire to a left front position, severe damage may occur so please keep them same side rotations.
Also have your wheel alignment checked at a tire shop each time you bring it in for a wheel/tire rotation as pot holes, hitting curbs,etc all can effect the way the tires wear if the alignment goes out.