If you would like a DISigner to DISign one for you then you just need to provide the name you want to appear on the license plate, month you'll be at WDW, and the theme/character you desire. You should read the STICKYs at the top of the forum for all the rules and request guidelines.
After you have received your DISign you print it and cut it out. Then, take it to a place like Office Max, and they will laminate it for you for just a couple dollars. I used ribbons to hold my license plates on our strollers.
I hope this helps,
Dee