Fun (Constructive) Things to Do w/ an Old Computer

I’m about to aquired a friend’s Mac PowerBook G4, and I’m trying to figure out something cool to do with it. As you may have figured out, I’m not all that technically savvy, but I like trying to do things I have no fucking clue how to do, like running a website.

Anyway, I looked into running Ubuntu on it, which would be kind of cool, or even to turn it into an Ubuntu server, which would be very cool. Really, making it into any kind of server would be cool. The downside of those is that a lot of the computer’s functionality depends on Mac OS X.
Other potential cool things would be somehow integrating into my appartment (like, controlling my lights or my stereo via the internet).

That’s just to give you some idea of what I mean by a ‘cool’ thing to do. I also know I don’t want to break it, though I do plan to take it apart/out of its shell. Other than that, I need someone’s doing-cool-stuff-with-old-computers expertise to inspire me.

Putting Ubuntu or Fedora on it would be cool. Even an older, slower computer will do a good job with Linux. You could use it as a server or a firewall, too.