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

In the example it looks like the state textbox and validator control are enabled or disable on selection of the country.

The Country dropdown has "Enable AutoPoastback" set to true it looks like. The postback form selection changed for that control either enables the state field and validaton control or disables it. Looks like the validation control has some extra code to change the textbox color too. Similar to what I do with my controls except I actually hide them too. I see postback everytime the control is changed so there is no Ajax involved which makes it straight forward. :)

Yep.. not too hard to implement.. :)