Snow Leopard System Requirements:

• A Mac with an Intel processor (PowerPC G3, G4, and G5 are no longer supported)
• An internal or external DVD drive, or DVD or CD sharing
• At least 1 GB of RAM (I would suggest 2GB minimum)
• A built-in display or a display connected to an Apple-supplied video card supported by your computer
• At least 5GB of disk space available, or 7GB if developer tools are installed

Upgrade to Mac OS X

This is the easiest and quickest way to upgrade to Snow Leopard. You simply run the installer right over your current OS X installation.

Step 1. Backup your drive before any installation.
Step 2. Insert the Snow Leopard install disc
Step 3. Click on the install Mac OS X icon
Step 4. In the pane where you select a disk, select your current Mac OS X install disk
Step 5. Click on the "Customize" button to select or deselect optional software installs. This button is important if you want to install Rosetta or Quicktime Pro 7, as these are not installed by default. You will need Rosetta installed for your older PowerPC apps to function properly.
Step 6. Click install. When the install is complete, the computer will automatically reboot.

Erase and Install

This option, also known as a ‘fresh install,’ completely erases the destination volume, then installs a new copy of Snow Leopard. Being that Snow Leopard is a major system upgrade, you may want to choose this option -- especially if you've been experiencing quirky problems with your current system.

Doing an Erase and Install may take some time to set up your computer after installation. You will have to configure all of your computer settings, install your third-party and iLife applications, and restore your personal files from the backup you made in Step 1 above. You can opt to use the Migration Assistant to help you with this.

One install option previously available on the Leopard install disc, is no longer available on the Snow Leopard disc. Can you guess what it is? It's the Archive and Install option. If you need to reinstall 10.6 down the road, it automatically archives and installs for you. Also, there is no "Previous System" folder at the root level after reinstalling.

Finally, to get information on "Upgrading using another computer’s optical drive," "Using Time Machine to back up and restore your system" or "Restoring your computer to factory settings," see the Installation Instruction pdf on the install disc.

UPDATE: Some people have questioned if you have to spend $169 to upgrade from Tiger to Snow Leopard. The answer is no. Walt Mossberg of The Wall Street Journal has revealed that those who have been hesitant to upgrade their Mac will be able to take advantage of Snow Leopard's bargain price, without the need to install the intermediate Leopard operating system first.

"For owners of Intel-based Macs who are still using the older Tiger version of the Mac OS, Apple is officially making Snow Leopard available only in a "boxed set" that includes other software and costs $169," Mossberg said. "The reasoning is that these folks never paid the $129 back in 2007 to upgrade to Leopard. But here’s a tip: Apple concedes that the $29 Snow Leopard upgrade will work properly on these Tiger-equipped Macs, so you can save the extra $140."

This means you can make a full install after you erased your disk, like I referred to above.