A PHP File up loader with progress bar - Online Docs.
The docs haven't kept pace with the development of Mega Upload. The newly added FAQ takes a look at the perl and JSP editions.
The documents on this page are the most recent versions of the documents distributed with the source tarball.
The project page on sourceforge.net contains a few message boards that provide additional usefull information. You can use these forums for posting your own questions as well. If you write to the author direct you may not get an answer.