i have a 2 combobox and a 1 textbox and a search button

1) country combobox
2) state combobox
3) textbox

when user click on search button without entering anything in the textbox then i'm inforcing user to enter (1) country and (2) city name (first 3 characters) which works great but i have a new requirement:

when the user select country = "United States" then i have to make sure user select

1)Country
2)State
3) city name (first 3 characters)

how do i do that?

the best example is here

http://www.peterblum.com/vam/DemoAll.aspx

when you select "united states" or "canada" the STATE required field is popup

same exact thing i want to implement