Dan over at PPC Luddite posted a great intro tutorial on how to use your Mac as a server.
Granted, this is an area where a basic install of Debian or some other GUI-less Linux can excel, even on a Power Mac G5. You’ll have more secure and recent versions of various kinds of server software, get more performance out of your machine, and can fine tune every aspect of your computer’s connection to the outside world. With Mac OS X Leopard, you have a great number of components built-in that can get you started, but they tend to be much older versions of server favorites.
As an addendum to PPC Luddite’s post, another option is to install XAMPP.
XAMPP is a combination package of great server components like Apache, MySQL, Perl, PHP, and so on. Combined into a single install, XAMPP makes it easy to setup test environments to see how websites and complicated scripts work before you put them on an external server. Of course, you could use XAMPP to turn your Mac into a nice file or database server, if you wanted. The nice thing about it is that it comes with plenty of documentation and built-in features, like phpMyAdmin, which allows you to create, edit, and delete databases from your favorite web browser.
Again, the benefit of XAMPP is that it is just a folder that you copy to your Applications folder on your Mac. You can easily delete it without mucking up anything else. You aren’t installing over your base Apache that comes with Leopard (or Tiger). You can run or turn off services as you need them using the simple GUI that comes with it above.
The downside is that while XAMPP provides some newer server software, such as PHP and mySQL, it’s still outdated. Leopard features Apache 2.2.17, while the latest XAMPP for PPC runs Apache 2.2.14. If you want the latest and most cutting edge, you might want to try a setup using homebrew or fink. Or just give your preferred version of Linux a shot.
The last version of XAMPP to run on PowerPC machines is 1.7.3. You can get it from Sourceforge here.