how to add a field that can be displayed on specific form??

Hi all,

I need to add a lookup field in CustTable form.

Now in Accounts Receivable -> Customers _> there location customers, end customers  . both have 'CustTable' form when u click on a customer .

Now my field should only shown when clicking the customers in end customers.

it should not be there when u open location customers.

Pls Advice me