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Most of us face the prospect of upgrading our operating systems with a mixture of excitement and dread. True, a new OS brings cool new ways to work. But that doesn't change the fact that when you install a major version of OS X you're essentially gutting your Mac and replacing its virtual insides.

Luckily, Apple's improved the upgrade experience with each new cat, making the process much less daunting. But despite the Installer's useful guidance, there are things it doesn't tell you, and places where its help falls short. With that in mind, here's my guide to making the upgrade process as trouble-free as possible.

What You Need

Before you get started, the two most important things you need are a compatible Mac and a complete backup of all your data. Leopard requires a Mac with an Intel or PowerPC G4 or G5 processor; a DVD drive; built-in FireWire; at least 512MB RAM; and at least 7GB of free hard-disk space. (I recommend at least 1GB RAM and 10 to 15GB of free disk space.)

To protect yourself from mishaps, I recommend you clone your hard drive instead of just backing up data piecemeal. You can create a clone-a complete, identical copy of your Mac's hard drive-using a utility such as Shirt Pocket's $28 SuperDuper, Bombich Software's Carbon Copy Cloner, or even OS X's own Disk Utility. If anything should go wrong with the upgrade, you can start up from the clone, restore it back to your main hard drive, and be back where you started with nothing lost but time. (For instructions, see Easy Mac Backups.)

Before You Begin

Before starting the installation process, here are a few steps you should take:

• Double-check your backup. Make sure you can boot from it by actually restarting your Mac using the backup as the startup drive.
• Check vendor Web sites to see if the software programs you use the most are compatible with Leopard--this includes Login Items (in the Accounts preference pane), third-party preference panes, and third-party system add-ons. If new versions are available, download those and keep them handy for installation after the upgrade. (You can install them before upgrading to Leopard, although some may require re-installation afterwards.) Macworld recent ran an excerpt from Joe Kissell's Take Control of Upgrading to Leopard that covers this area in greater detail.
• Decide which installation method you want to use. Verify and, if necessary, repair your hard drive using Disk Utility. You can access this tool from the Welcome screen of the Mac OS X Installer-choose Utilities -> Disk Utility.
• Verify and, if necessary, repair your hard drive using Disk Utility. You can access this tool from the Welcome screen of the Mac OS X Installer-choose Utilities -> Disk Utility.

See Our Complete Leopard Coverage