After installing OS X 10.3 and various software updates (Keynote, iSync) which were made availabe by Apple after 10.3, I found out that the installed updates were not displayed in the Software Update PrefPane. I thought "Oh no, not again!" Apple did the same bug as with the update from 10.1 to 10.2! But this time it is different. With 10.2, software updates were not displayed when the permissions of the software update log were wrong. With 10.3, they are not displayed when the format of the log file is wrong. And the format changed with 10.3!
So to fix this, you have to navigate to /Library/Logs/ and edit Software Update.log in your favorite text editor. Remove all lines from updates that were installed before 10.3. You should end up with something like this:
2003-10-24 18:56:14 +0200: Installed "iSync" (1.3)Save the log file. Go to the Software Update preferences panel and you will see your software updates again!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031025054641612