Please help a newbie

Hi, I'm trying to create an extremely simple registration form to embed within my moonfruit created website. I need to capture basic name email which is fine, but I also need to get people to select from a pre populated list of schools. As there are over 16,000 in the UK I need people to be able to to first click on their county. This will then bring up only schools which are within that county. Can someone tell me how to do this?