@Aegis
not sure why this isn't included, but try installing the PNG icon module from os4depot.net (
download link). you'll need to install it in LIBS:IconModules and restart workbench. i remember doing this on my SAM years and years ago, but i haven't had to on any of my machines since. i wonder if it wasn't included in the classic version for some reason? no idea.
as for third-party libraries, loads of OS3.x software requires the same in my experience. was there some specific software you were referring to?
edit: cgutjahr beat me to the submit button. heh.
-- eliyahu