James, we have a doggie door that fits with our sliding glass door. I got mine from my aunt but I've seen the exact same one here...
http://www.petsmart.com/global/produ...t=dog+door&N=2
I let mine roam freely...but the puppies are still in the x-pen. They are too young and although one is able to get back and forth through the door, I don't feel comfortable enough to give him free roam.