用ajax更新colorbox

I am very new to using AJAX, basically this is my first project, and i'm kinda clueless to what the best way to approach this would be.

The scenario and what i want to accomplish. Currently i'm opening a form with a select list, in the "lightbox" plugin colorbox. Now with one of the options form the select list i need to redirect the client to a form with a textbox and from there execute my php.

Basically this is what i wish to accomplish:

• Load all the content inside the same colorbox frame.
• Redirect clients to a textbox form.
• Return the result of the php code i've executed after the forms has been submitted.

I would really appreciate if a kind soul could guide me in the right direction, to what i have to do to make this work.