Return Listbox Results On Double Click

This is probably failry simple if you know what you're doing, but I don't know what I'm doing....

I have a form (Purchase Orders) and on that form there is a search button to allow the user to search the customers table by customer name. When the user clicks the search button a search form opens and the search results (customer number, first name, last name) populate a list box named "lstCustInfo". How can I set the list box double click event to return the customer number, first name and last name to the Purchase Orders form? To make it even more complex I would like to return the data in two fields: customer number and LastName, FirstName. The problem with returning the results in two fields though is that I need to be able to break it into three to save it in the customers table because the table has a place for Customer Number, First Name and Last name.

Does anyone have any suggestions? Is there a better way to do this than returning 2 fields and having to break it back into 3 to store?