Dependant select in profile

[Kriminal]

HI!
I wondering if you could help me to introduce the following change to my forums: I need to create one combobox which depends on other one. For example, I fill the first one with the list of countries and when the user selects one item (a country) the other one is filled out with the list of states from the selected country.

I know how to do that in regular web pages, but I can't find the way to do this in vBulletin... If I add profiles fields (country and state) via AdminCP, they appear in user profile page, but I don't know how to "connect" them.

I really need to do this, if you could help me i'll really appreciate it.

Thanks a lot!