Downgrading from the Mac® OS X 10.2.8 Update to Mac OS X 10.2.6
Apple® has posted suggested workarounds for the Ethernet-related problems introduced with the Mac OS X 10.2.8 Update in the AppleCare® Knowledge Base document "Mac OS X 10.2.8: Can't Connect via Ethernet After Installing Update."
If these instructions do not resolve the problems you are experiencing with the Mac OS X 10.2.8 update, you can downgrade to Mac OS X 10.2.6 using the following procedure.
You will need...
Your Mac OS X v10.2 Install Disc 1 and 2 CDs.
- Perform an Archive and Install with the Preserve User and Network Settings option. See the AppleCare Knowledge Base document "Mac OS X 10.2, 10.3: About the Archive and Install Feature." 
- Repair Permissions from the Mac OS X v10.2 Install Disc 1 CD -- not the hard drive -- as follows:
- Boot from your Mac OS X v10.2 Install Disc 1 CD.
- When the Installer window appears, select Installer > Open Disk Utility from the Apple menu bar.
- When Disk Utility opens, select your Mac OS X startup disk from the list of drives and volumes.
- Select the First Aid tab.
- Select the Repair Disk Permissions button.
- After Repair Permissions completes, Quit Disk Utility. Focus returns to the Installer.
- Quit the Installer. When prompted, select Restart.
- Delete the Previous Systems folder using the instructions in the AppleCare Knowledge Base document "Mac OS X 10.2: How to Delete a Previous Systems Folder."
- Apply the Mac OS X 10.2.6 Combo Update. See the AppleCare Knowledge Base document "Mac OS X 10.2.6 Update Combo: Information and Download."
- Repair Permissions using Disk Utility on the hard drive, per Step 3, "Repair Disk Permissions," of the Resolving Disk, Permission, and Cache Corruption FAQ.
 The Applications folder is preserved -- copied intact -- as part of the Archive and Install process. However, per the AppleCare Knowledge Base document on Archive and Install, it states in the Notes section:
"2. Some third-party software items may not be preserved. If third-party software doesn't work after the Archive and Install is performed, reinstall it or contact the vendor."
Accordingly, you may want to review the article "Migrate to OS X 10.2 with a Clean Install" from the October 2002 issue of Macworld for additional information, in particular the section therein concerning the Library folder. While this article was written to advise users upgrading from Mac OS X 10.1.x to 10.2, the additional details it provides on Archive and Install may prove useful for anyone using such.