After playing with the keyboard type (I don't remember exactly what I did) I had a nasty keyboard type/mapping problem on my MacBook Pro (Max OS X Leopard 10.5.1):
From some point on the two keys (<> and ^° in my case, german keyboard) where swapped. All other keys were normal, so it was not a keymap problem. The german keymap worked well except for these two keys which were swapped. Stangely enough the button to undo this change 'Change keyboard type ...' *vanished* from the System Preferences! I could not believe this until I verified that on other Macs this button is present. I don't understand why. Apple: Never do these configure once things!
Starting the KeyboardSetupAssistant did not help at all since it would say that all known keyboard were configured. Thanks.
I found the solution in some Apple forum thread but I am replicating it here since it took me quite some time to find it although it looks quite obvious to me now:
1) Delete the file: /Library/Preferences/com.apple.keyboardtype.plist
After removing the file and restarting:
1. I could set the keyboard type correctly using the assistant and
2. I can now change the keyboard type again using the System Preferences
I don't know why this button was missing before ...