Check Script - http://www.ninethsense.com/content/view/48/51/
You need to duplicate the line:
imagestring($im,2,10,0,$_REQUEST['txtText'], imagecolorallocate($im,200,200,200) );
and change the X and Y axis.
Syntax:
imagestring ( resource $image , int $font , int $x , int $y , string $string , int $color )