Apple will be releasing OS X Mountain Lion soon. There are a number of things you need to do to get ready for this new OS, including making a current backup of your data, and upgrading to Snow Leopard or Lion, if you haven't already.
One important task that is often overlooked is a hard drive checkup. Before you upgrade to a new OS, it's important to ensure that your drives are in good working order.
It's not uncommon to use a Mac day in and day out, and not be aware that the startup drive or data drive(s) have errors that can lead to trouble down the road. I always recommend testing drives for errors every now and then, even if you're not upgrading your OS.
There are a couple of ways to check your Mac for drive errors; the easiest is to use Disk Utility, which is included with the Mac OS. You can find step-by-step instructions in the following guide, which covers both how to check for drive errors and how to repair them.
If your drive has errors that Disk Utility can't fix, you can try one of the many third-party applications available for testing and repairing a Mac's drives. The three most popular utilities for testing and repairing drives are:
Getting your drive in tip-top shape is a must before you install a new OS. Take the time now to test and repair your drives; you'll be glad you did.