Non-developer needs help!  I am trying to create a custom button with javascript to create records on a list view.  The new records are Invoices that are details of master-detail relationships to Programs and Accounts.

The Create New Invoice button is on the Programs list view.  The Account is a lookup field within the Program and it is called Billing_Account__c.  The button will work if I hard code a Account Id into "newInvoice.Billing_Account__c = "xxxx";" but otherwise I can't get it to work.  Any ideas?

Also, are there any other best practices that I should incorporate in the button, such as "8 Programs were selected, but only 4 Invoices were created."?

Thanks in advance.

{!REQUIRESCRIPT("/soap/ajax/27.0/connection.js")}
var url = parent.location.href;
var records = {!GETRECORDIDS($ObjectType.Program__c)};
var newRecords = [];

if (records[0] == null) {
alert("Please select at least one record to update.");
} else {
for (var a=0; a<records.length; a++) {
var newInvoice = new sforce.SObject("Invoice__c");
newInvoice.Program__c = records[a];
newInvoice.Billing_Account__c = "{!Program__c.Billing_AccountId__c}"; //This line is the problem
newRecords.push(newInvoice);
}
result = sforce.connection.create(newRecords);
parent.location.href = url; //refresh the page
}