Those modules should also be available via anonymous CVS:
http://www.abisource.com/dev_download.phtml
Go to the directory where you've got the abi tree installed, and follow the
directions at this URL for accessing the abi module, but in the third step,
type:
cvs checkout libpng
cvs checkout zlib
Thus, your directory structure would look like the following:
cool_projects
abi
libpng
zlib
With Jeff's latest makefile tweaks, all you need to do is type make in the
abi directory and it'll find and build everything from there.
Paul