temporaneità

Someday this post could save you an hour: do you need to use JToolBarHelper::custom() within Joomla 1.5.x? The icons that it calls by default are placed in administrator/templates/khepri/images/toolbar/ (substitute khepri with the name of your non standard administrator template if you have one) and if you want to use, for example, icon-32-help.png, you have to write something like
JToolBarHelper::custom('up0', 'help.png', 'help.png', 'up', false);
In other words, you have to pass the filename without the starting icon-32- string. If the previous case is not sufficient for you and you want to pass to custom() your custom icon, read this post.