I never downloaded the link on top, but as noted earlier, mpj is one of the original devs, who released the source here on his forums: http://www.insane-gamers.com/forum/showthread.php/6902-L2-NET-Source-code
I tossed the project onto https://github.com/Xackery/l2net and will be breaking and fixing things, since I play on my own private server with friends and enjoy the bot.
Feel free to create issues, fork, do pull requests, and all that jazz.