Is it possible to upgrade a "ClamShell" iBook to OS X

Possible, but that's about all they'd be able to do. Installing almost any application on it will be slow. 10.3.9 is the maximum OS that a Clamshell will support. Clamshells with Firewire are a little better than the green Clamshell, as then backing up is easier and faster. With Mac OS X, you want some form of fast backing up speed. USB 1.1 is the only USB that the Clamshell has. It is fine as a Mac OS X internet machine, but limited RAM upgrade capacity, and hard drive capacity will limit it when doing much of anything beyond holding music and simple word processing. And if it is the 300 Mhz version, hard drives larger than 8 GB may have to be partitioned.

http://docs.info.apple.com/article.html?artnum=106235

A firmware is needed before updating to 10.2 or later:

http://docs.info.apple.com/article.html?artnum=86117

Previous versions of Mac OS X are nearly unusable because of lack of application support.

P.S. The clamshell iBooks are the iBook (Colors) (links to forum of same name) iBooks, and not the dual USB model.

a while back on another forum a poll was taken on what was the best os for clamshells and the winner was 10.3.9. that's what i run on my clamshell and i have no problems. during installation you can save a lot of space by not instaaling all the printer drivers and foreign languages.

I have to agree with britny's post. I had a Tangerine iBook that I upgraded to OS 10.3.9 and installed a larger HD. It had Airport and worked like a champ. My son and his girlfriend had a great time taking it into wifi cafes. Totally retro.
Now a writer for a charity org. uses it and surfs off her neighbor's wireless, with permission.
Richard

In my opinion, upgrading the hard drive is crucial to the success of running OS X on a G3 computer. I wouldn't want to run OS X on anything less than a 30 GB hard drive. Many do, of course, but running OS X on less than a 30 GB hard drive requires vigilant and almost constant maintenance of the hard drive. I don't want to have to worry about that all the time, so I leave my 500 MHz iBook with its 10 GB hard drive in OS 9.