AJAX observer on select form

Hi, I was hoping someone might be able to help with this one. I've got a select list that I probably need to use an observer on. I want the list, whenever something is selected, to show a hidden div based on what's chosen. Basically people choose between cash, credit, or check, and then when they pick it will show a different div asking for more information. Any ideas?

Oh, and I know I can probably just use any Javascript to do this, but I really don't like javascript cluttering my code if there's a way I can write it in Ruby's prototype/scriptaculous.

observe_field or set the select's onChange to a remote_function ?