Check Custom field to flag an invoice

Hi,

Heres the scenario:

I created a custom field on the customer main screen called 'custentity43', Labeled: "Consignment" - it is a check box (yes,no).

I would like a pop up to appear when a user creates an "Invoice" that says:
"Hey this is a consignment account"

So I created a "Before Load Function" as follows:

 function ConsignCheck_BeforeLoad()  {  x = nlapiGetFieldValue('custentity43');  if (x == "T") {  alert("this is a consignment account");  }  } 

I don't get an alert... something tells me I have to load the customer record first, how?

2. If I don't load the customer record first, does the current invoice knows to go to 'custentity43' of this customer?