I have 5 dogs and I have potty trained each and every one of them by crate training and following this schedule:
http://www.darnfar.com/Dog%20Trainin...ng_a_puppy.htm
The key is to getting a crate that is only big enough for them to stand up, turn around, and lay down. When they are laying down, the whole floor of the crate should be covered by their body. If you buy the smallest crate and it is still too big, you can put a box in the back of it. That is how I potty trained all of my dogs and they were all potty trained within a month. After they are potty trained, you can take the box out of the crate or buy a bigger crate that is more comfortable but it is essential to have the proper size crate while crate training/potty training.