I have a Purchase order form, that works really good. There is a subform in this purchase order with the following structure.

Reference (lookup to Product Catalogue)

Description

Cost

Quantity

tax

Total Cost

Status (dropdown with 3 choises: approved, disapproved and pending)

Now, I am working on a Purchase Request form that has a subform with this fields.

Reference (lookup to Product Catalogue)

Description

Quantity

Status (dropdown with 3 choises: approved, disapproved and pending)

I would like that the Reference Lookup in the Purchase Order only to show the products that where previously requested trough the Purchase Request form. I also would like to automaticaly update the status when they are approved or disapproved in the Purchase Order. 

How can I do this? All hints, Ideas or Clues are welcome.

Any help will be appreciated.