Filter a lookup field based upon selection done in another lookup field in the same form

Filter a lookup field based upon selection done in another lookup field in the same form

Hi,
I would like to implement the same behaviour that I see in the application "Order Management 4.0" already available as a template. I'm referring especially to the form "New Product" in which the user selects the "business Group" item and according to this choice the "Product Group" field is filtered.
How is it implemented? I tried to reproduce that behaviour without success.
Thanks