Lisas,
I want to check in on this "maintenance" bit. Since I service them I consider myself qualified to comment.
If it has moving parts it needs servicing. You're prudent to ask. I have several clients that have not had service on their machine(s) for three years of more. An ounce of prevention is worth apound of cure.
Some of the older Mac cases tend to collect a significant amount of dust. Dust and electronics components, not a good marriage. the iMacs will be more difficult to service in this regard while the mini towers are a breeze in terms of access.
Depending on your usage - how often you are opening and saving, rewriting files, doing large scale file operations (photoshop etc) you should Zap the PRAM and rebuild the desktop. Both apply in OS 9.x or earlier while only zapping the PRAM applys in in the OS X architecture.
Compresssed air for your keyboard cause no matter how much I tell you not to eat over the thing, you will. I've pulled some pretty haneous things out form under those keys.
Every six months or so you should run a disk utility. I prefer Tech Tool Pro. Or you can simply run boot up from the install CD and run the native Apple Disk First Aid on the boot volume.
And of course the "clock" battery does need replacemtn every once in a blue moon. In OS 9.x you'll notice your date and time doesn't stay still even after you set it. That's an indicator.
Otherwise, you are squared away. The Dodge Dart of computers.
MacGeneral