How to assign a paper size to an XML template?

We are trying to set up an xml template to print checks on legal size paper.  How do we assign the paper size?  We've tried doing it when creating the form in Word but it still comes out on letter size paper.

10/28 - Forgot to mention that we are on R12.  I don't think it's a printer isssue since we've tried it on different printers that all have legal paper assigned to one of thier bins.  When we print the template itself from Word it prints on legal paper but not from the application.