Access 2007

My datadase consists of a list of our equipment. When you click an "Open" hyperlink in the table, that equipment's information file form opens in pop up view. In this form you can edit the equipment's information like make, model, and serial number. On this same form is a tab control area, which contain some subforms (children) linked to the main form (parent) by primarykey/foreign in a 1 to many relationship. An example of a subform is Engine. Basically that subform shows (only select field) in data table view all the engines attached to that piece of equipment basically as a read only preview. In order to add/edit that engine information, you have to double click on the record in the subform. Now a pop up form that allows you to edit/add the records is opened.

Herein lies my problem, I cannot for the life of me get the pop up engine form to link to the main equipment information form by the way of foreign key/primary key. Original I had everything add/editable on one form using subforms and everything worked fine, but then the subforms started needing subforms and so on. Needless to say the form became overwhelming and popups don't seem as overwhelming. I just need to get the "linking" straight.