It's a smart idea to ask for advice as to how to keep your Powerbook working safely for a while, but it's a better idea to ask for specifics. I'll get you started with some Dos and Don'ts about your Powerbook:
Do:
Update your Powerbook to the latest version of OS X, and keep it running the latest version of OS X until Apple releases something newer. Currently,
this is the latest version - 10.3.4.
Similarly, keep all your Apple software up to date. That includes:
Quicktime,
iTunes, and Mac OS X, as mentioned straight above. Also, check for updates every so often. If you're on a low-speed connection (such as I am), keep all of your downloaded software organized and in folders of their own.
Don't:
Do not install alpha or beta software if you don't need it, or unless you're feeling really lucky. One of the fastest ways to "screw up" any computer is by installing too much buggy software, or software that hasn't been fully tested and debugged properly.
Do not use Software Update (located in: System Preferences > Software Update (third row)) to update your software. Software Update sometimes has problems connecting to the Apple server, and it sometimes deletes downloaded packages on you. Instead, go
here to download the latest Apple software. Get to know that link, and keep it memorized it after you have typed it in enough times. But if Apple has announced new software that is available via Software Update but not the downloads page, then use Software Update.
Do not allow your Powerbook's battery to run all the way down to zero! That will hurt your Powerbook's battery life. Keep it charged and above 10% at all times, or you might lessen the capacity of the Li-ion battery. If it happens once in a while, that's fine, but constantly draining your Li-ion battery is not recommended.