Use an after update event for the list box. Here is code I use for the same thing on a sales order form.
ChaZ
Private Sub CustomerNumber_AfterUpdate()
Forms!so_head!Name = DLookup("CustomerName", "Customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!Address1 = DLookup("Addressline1", "Customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!Address2 = DLookup("Addressline2", "Customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!City = DLookup("City", "Customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!State = DLookup("state", "customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!Zip = DLookup("Zipcode", "customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!Contact = DLookup("Contact", "customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!Phone = DLookup("Phone", "customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"
Forms!so_head!ShipName = DLookup("ShipName", "Customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!ShipAd1 = DLookup("Ship1", "Customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!ShipAd2 = DLookup("Ship2", "Customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!ShipCity = DLookup("ShipCity", "Customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!ShipState = DLookup("Shipstate", "customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!ShipZip = DLookup("ShipZip", "customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!ShipContact = DLookup("ShipContact", "customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

Forms!so_head!ShipPhone = DLookup("ShipPhone", "customer", "Customernumber='" & Trim(Forms!so_head!CustomerNumber) & "'"

End Sub
Ascii dumb question, get a dumb Ansi