Hello Rebecca,
I had/have the same problem. To determine which version I needed, I took the pad apart. The version number is printed on the digitizer element - the flat brown/orange plastic filaments attached to the screen. You first have to move some sliders inside the ports that connect to the docking station, using a small screw driver ("-"; a "+" will not grip well) to push the sliders sideways until they click and an arrow shows. You can find more instructions here: [guide|10306]
After that, I used an old credit card to detach the screen from the frame, since the screen is mostly held in place by double-stick tape. I also remember 4 small screws ("+") that I had to take off, though that may have been to remove the LCD underneath the glass panel.
You don't have to detach the digitizer from the frame, just look for the small white(?) print on it. One of the numbers there is the version of the digitizer. Mine was a 5148.
The 5184 version seems to be in high demand - I am still waiting to hear from a supplier who is trying to get one. Apparently the three different versions are not compatible, so you do have to make sure to order the correct one.
Good Luck!
thomas