how to use select box relating with database(oracle) in ruby on rails

hi guys

i am using ruby on rails since 2months and the version for rails is
2.0.2 and the editor using is APTANA IDE and the problem is i have to
use selection box in a page so that when i click on any one of the
items in that selection box it will show the details of the related
item in another select box.

for that i created two models one is
category(category_id,category_type) and another is tech_type.And how
to write code in controller and view to get the result