Separate page.tpl file for URL
It's based upon the path.  In D6:

page-testpage-get.tpl.php

In D7:

page--testpage-get.tpl.php

(Although D7 might want page--testpage--get.tpl.php due to its love of double dashes :)

All about templates and their suggestions can be found here:

D6: http://drupal.org/node/1089642

D7:  http://drupal.org/node/1089656