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.

Carlo,
You saved me the promised hour.
Very much appreciated!
There were lots of other twists and turns in the road. Narrative and screen captures here:
http://moleski.net/dokuwiki/doku.php/blog/rsg2
I’m a little weak in Italian–OK, not far from completely cluess, if truth be told. I find myself wanting to say “Molto bene! Grazie!” Or something to that effect.
Marty
Martin: you are welcome. “Molto bene! Grazie!” is correct Italian and its effect is fine. :)
Grazie Signore! It saved me an hour as well.
[...] Temporaneità [...]
Saved me an hour as well. Thanks a lot!
Thanks buddy! It’s really a time saver.
thansk much, make that like 4 hours saved.
don’t quite understand why system level functions such as a toolbar would be tied to a template.
Wow thanks for that. It is very unclear how to do that in J!’s documentation.
thank you so much for sharing your knowledge. i helped me alot and saved a day :)
it save me an hour as well :)
ty very much!!!!!!!
Using custom icons: http://docs.joomla.org/How_to_create_a_custom_button
Thanks: that link didn’t exist when I wrote the post.