AJAX :: PopUp A Form When A Text Field Is Clicked On?

I have looked all over the Internet for the last few hours and the main articles I can find are using JQuery or Prototype to handle validation. However, I am trying to work on a series of forms (They won't work with tabs due to their nature) which depend on other items in a database.So, what I want to do is if someone is inserting a record in Form 1 to input into Table 1 which has an ID from Table 2, it will pop up a new form (shadowing out Form 1, sort of like LightBox does) to create the new record into Table 2. Once this record is inserted successfully, it will return control to Form 1.I plan on making an OnKeyUp activate this script when someone clicks on the textfield to add a new category. I understand what I have posted may be a little confusing, but I basically just need to be pointed in the right direction with a couple of tutorials to follow for how to use AJAX to show forms.