Looks like you just have the input box and text flipped around, right?

Find this code:

        echo( '<p><label for="securitycode"><small>Enter the word in the box (required)</small></label>'."\n\t\t\t\t" );
        echo( '<input type="text" name="securitycode" id="securitycode" size="22" tabindex="4" />'."\n\t\t\t\t" );
        echo( '<input type="hidden" name="matchthis" value="' . $cas_antiselect . "\" />\n\t\t\t\t" );

And rearrange it like so:

        echo( '<p><input type="text" name="securitycode" id="securitycode" size="22" tabindex="4" />'."\n\t\t\t\t" );
        echo( '<label for="securitycode"><small>Enter the word in the box (required)</small></label></p><p>'."\n\t\t\t\t" );
        echo( '<input type="hidden" name="matchthis" value="' . $cas_antiselect . "\" />\n\t\t\t\t" );

Let me know how that goes for you!