Validations

I don't got the problem with countrys's but with numbers and payments. I also wanna select a list in validation thats working now. But can i add an action to a selection within the box. for example when i select bank in a list a sum has to be placed in a sertain cell how can i do that ?

HELP??

I have a list of countries (USA, Australia, England), and a list of cities. How can I make than when the user selects USA in one cell, in the other one appear only cities from USA (New York, Los Angeles), and also for Australia (Camberra, Perth), etc. ?"