Hello,
You should be able to access the DVD settings through the console.  There, you should be able to select which screens on which you would like the DVD to show.  Your best resource for this one would be the user manual, as (if I recall correctly) they have some excellent diagrams for the system.  If you have lost your manual, you can find them relatively inexpensively on eBay.  Here is a link to get you started: http://search.ebay.com/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.com%2Fws%2F&fkr=1&from=R8&satitle=2003+trailblazer+manual&category0=&submitSearch=Search
Best of luck!
CarGrrl
Best of luck!
CarGrrl