How to build a database?

Hi,

Im trying to create a simple database to store information about hotels and airports in different countries. So first I have a dropdown list of "continents" so if I choose "europe" then on the next dropdownlist I would only like to have the countries of europe coming up. Then you have the cities of that country and if you select "other" you can manually type in the city.

Then I also would like to have the feature that if I select a city that someone already have added information about. a text will state "there is already information about this city please edit this city in the city view"

Is this complicated? or doable?
efspilot