Original text of the following tip due to Macology and Ronda Wilson.
This is a brief tutorial on how to improve YouTube video playback on an Apple iBook G3. As of now, I have only tested this method on my own iBook. iBook's iBooks with lower specs than the 900 MHz model may not receive the same performance upgrade from this brief tutorial. With that said, here is what you can do to attempt to make YouTube more functional on your iBook G3.
1) If the iBook is running Mac OS X 10.4 (Tiger), disable Dashboard and Spotlight:
While widgets are fun and Spotlight is a useful quick search tool, they are known resource consumers that make video playback problematic for older Mac laptops, such as the iBook G3. To accomplish this, you will have to use Terminal (Applications > Utilities > Terminal). Once Terminal is open, enter the following command
defaults write com.apple.dashboard mcx-disabled -boolean YES
After entering this command, you will then need to restart the Dock (Dashboard is owned by the Dock). To do so, again, using Terminal, you will enter the following command.
You may still see the Dashboard icon in the Dock, but clicking on it should do nothing.
For the next part, you will use Terminal to disable Spotlight. Open Terminal and enter the following command.
sudo nano /etc/hostconfig
This will bring up a configuration listing. Use the arrow keys to scroll down and change the value, SPOTLIGHT=-YES-, to SPOTLIGHT=-NO-.
From here, you should press Ctrl+X to exit, upon which it will ask if you want to save. Follow the on screen prompts to save, and exit out of Terminal. Spotlight will still appear in the corner of your screen, but it won't search for anything. Now on to the next step.
2) For any video URL on YouTube, add &fmt=5 to the end of the URL, and this will force videos to run in quarter VGA mode (320x240). The video quality will be degraded, but you should maintain a stable frame rate that is uninterrupted and capable of streaming without the need to pause and wait for the entire video to load.
This method has worked for me for old and new videos alike. Unfortunately, I have not found a way to make iTunes/Quicktime force videos into a low resolution mode, so this fix will only resolve video playback involving YouTube.
To restore functionality to Dashboard and Spotlight:
1) How to Restore the Dashboard
Open Terminal and input the following command
defaults write com.apple.dashboard mcx-disabled -boolean NO
After entering this command, you will have to restart the Dock. To do so, enter the following command into Terminal
Now, can drag the Dashboard icon back to the Dock, or if you did not remove it to begin with, it should function once again.
2) How to restore Spotlight
Open Terminal and enter the following command
sudo nano /etc/hostconfig
This will open up a config file. Scroll down (using the arrow keys) to the portion that says SPOTLIGHT=-NO- and change the value so that it says SPOTLIGHT=-YES-
Exit the config file by pressing Ctrl+X. Follow the onscreen prompts to save the config file, and you are all set.
Best of luck to you all. I hope that this tutorial has been helpful.