I don't know if this is what you mean, but I think I had the same problem.
Eventually I found out (with some help) that in the includes folder there is a file called 'draw_functions.php'
In that file at line 201 you will find the following code:
$crs = $xoopsDB->query( "SELECT cid, title, imgurl FROM $table_cat WHERE pid=$parent_id ORDER BY title") or die( "Error: Get Category." ) ;
change the value after ORDER BY to what you want..
Hope this helps,
greetz Frank