There is a bug in Mac OS 10.2 (Jaguar)'s Screen Saver Engine. While it is running, your Mac cannot mount external media (CDs, etc.). If you try to insert a CD, your drive will spit it back out at you after a few seconds. If you run a screensaver as your desktop background (see this hint), you will notice this fairly quickly.
I spent four hours trying to troubleshoot my OS because I thought that the problem was linked to my recent deletion of the dock application. Turns out, there are no side effects from removing the Dock that caused the problem I was experiencing. So now I just turn off the screen saver desktop whenever I want to insert or eject a CD (I use CoolBackground v2.1). Hope this information proves helpful.
[Editor's note: I'm not sure if this is a bug or a feature - I think it could it be considered a security risk to allow insertion of a CD when a (possibly secured) screensaver is active. Either way, this is good information to know if you use the screensaver desktop feature in Jaguar.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2003020606102385