ich denke : this is possible by altering a little bit of code :
go to line 137 and following of garyscookbook.php
there you can change the code into this :
<?php
//Get the value of $my->id and $my->username
global $my;
//Get Current User from Joomla Global $my
$current_user=$my->id;
?>
<input class=\"inputbox\" type=\"text\" name=\"imgauthor\" value=\"<?php echo $my->username;?>\" size=\"50\" maxlength=\"100\" readonly=\"yes\" />
this makes the input field already filled with the logged in user.
