Binary package hint: pommed
Testing with Ubuntu 8.10 Alpha 4. Manually changed System -> Preferences -> Keyboard to "Apple: MacBook / MacBook Pro (Intel)", but no change. Apparently Ubuntu does not know what to do with the key second right to the space key (the key right next to the space key is the "Apple" key which also is right left to the space key) which should probably do the job of the AltGr key.
Fn - ctrl - alt - Apple key - SPACE - Apple key - strange key which probably should do the job of AltGr - < key etc.
Note that normally on modern Macs you get the "@" symbol pressing some key + the letter "l" key. At the moment, with Ubuntu, things work neither the Mac way nor the usual PC way. (I suppose it would be useful to use the PC way.)
This goes for a German keyboard tested. I assume it's the same with other languages' keyboards (English keyboards have th "@" on "q", too, right?).
"The MacBook Pro Keyboard doesn't have a Alt GR / Right Alt key, so there is no way to type Third Level Keys, such as "@" and "[" (these vary from country to country). Here is a solution:
Go to System > Preferences > Keyboard. On the Layout Options tab, select "Third Level Choosers" and check "Press Enter key on keypad to choose 3rd level".
Now you can use the Left Enter key (on the MacBook Pro keyboard) as a Alt Gr Key to access these Third Level Keys. "