Drop Down List auto-update with jQuery in asp.net mvc

If you have a form and the only parts in this form that you need ajaxified is two connected Drop Down Lists, how would be the best asp.net-mvc-like way to solve this?

Once the first DropDownList changes value the other DropDownList should be populated depending on the item selected i开发者_如何学运维n the first list. This is a fairly common task I would think.

So I guess I have to create the whole form as a Ajax-form, correct? But how would you handle the Posts / Results? I might need a little introduction to jQuery, Json and whatever is nessesary to solve this.

Manual approach - for when you need explanations.

jQuery plugin - for when you can use a ready solution.