Do you miss the MOSAIC screensaver that was in "Lion" 10.7 but removed from "Mountain Lion 10.8?" You can install it to run in "10.8" as long as you made/saved a copy of "10.7" OS on a CD or flash drive before you upgraded to "Mountain Lion" AND you have iPhoto installed with "Mountain Lion."

Note: The "old" PREFERENCE PANE (4.0) from "Lion" will replace PREFERENCE PANE (5.0) in "Mountain Lion" (i.e. both PANES cannot be used in the same OS). You can move/save 5.0 elsewhere within "Mountain Lion" - e.g. in your Applications Folder - or on a separate flash drive in case you decide you no longer want 4.0 and would like to switch back to the new screensavers which come with "Mountain Lion." Of course, switching back to 5.0 means you lose the 4.0's MOSAIC feature.

Steps:

1. Go to DISK UTILITY in your "Mountain Lion" computer or laptop.
Follow the directions to partition the drive. (Yes, you can now do this without first having to erase the whole drive and then partition.) 10 GB for "Lion" should be plenty.

2. Then, install "Lion" OS from your disc or flash drive onto the new partition. This could take 30 minutes or so.

3. When done, go to (you are still operating "Mountain Lion"):

/System/Library/PreferencesPanes/DesktopScreenEffectsPref.prefPane and move - actually remove, DO NOT copy or delete - this to some other location on your computer. (I preferred to move these to a new folder I created called MOSAIC 5.0 on a portable flash drive.) You will need to enter the Admin Password to authenticate the move of this preference pane.

4. Now, go to: /System/Library/Frameworks/ScreenSaver.frameworks and remove this to some other location on your computer (or flash drive in the folder called MOSAIC 5.0). Again, your Admin Password may be required to do so.

5. Go to System Preferences START UP and restart your computer in the new partition (i.e. "Lion").

You are now running "Lion." When you open your computer folder, you should see TWO hard drive images: one contains "Mountain Lion 10.8" and the other contains "Lion 10.7."

6. Retrieve the same two items above from the system's library in "Lion" and copy both to a disc or flash drive. (You could even try to simply drag these to the "Mountain Lion" hard drive icon and folders therein, but I felt more confident that these files were stored in a new folder called MOSAIC 4.0 on the flash drive.)

7. Repeat Step 7, BUT select "Mountain Lion" as your START UP.

8. Place these "Lion" 4.0 versions (from the flash drive) into the exact same locations from which the "Mountain Lion" 5.0 versions were moved:

/System/Library/PreferencesPanes/DesktopScreenEffectsPref.prefPane

/System/Library/Frameworks/ScreenSaver.frameworks

9. Restart your computer (which should still be in "Mountain Lion").

10. Go to System Preferences.

11. Select Desktop and Screensaver.

You have successfully replaced the "Mountain Lion" screensaver with the (old) "Lion" screensaver.

P.S. If anyone knows of a simpler way to accomplish this goal, please feel free to let us know. Thanks. :0)