http://support.apple.com/kb/DL1192
Mount the NetBoot9.dmg disk image. Right (Control) click on NetBoot.pkg in the language you need, and select Show Package Contents (from the contextual menu). A Finder window opens. Go into the folder called Contents, and then into Resources. Find the file called NetBoot.pax.gz and drag it to the Desktop (or any other location). This is an archive file.
Double-click NetBoot.pax.gz to have Archive Utility extract a folder called NetBootInstallation. When double-clicking the NetBootInstallation folder, you may get an error message about "access privileges." Right (Control) click on the folder and select Get Info. In the Info window, toward the bottom where it says Ownership & Permissions, set it to (You can) Read & Write. Now, open the NetBootInstallation folder.
Find the file called NetBoot HD.img and double-click it to mount this disk image. Inside the disk image, there is a System Folder. This System Folder is 9.2.2, and it contains all the components needed for any Mac that can officially boot Mac OS 9.2.2 or run it as Classic under Mac OS X.
Drag this System Folder to the root level of your Mac's hard drive. If you want the included Mac OS 9 apps, also copy the Applications (Mac OS 9) folder.
Run System Preferences and go to the Classic pane, select that System Folder for Classic. Click the Start button to run Classic. After a few messages about updates, Classic startup completes, and you can run Mac OS 9 apps.