Because the video on an external monitor connected to the iBook is only a Mirror, there is a distinct possibility that even though the card "might" be able to produce higher resolutions, the iBook screen cannot handle it and therefore everything is geared to the lowest resolution supported. To produce 1280 X 1034 on an external monitor, you would have to set the iBook to that figure. It is not available.
Example. I recently upgraded to a 17" Apple flat panel which is currently running at 1280 X 1024. The monitor that was replaced was the Apple 15" flat panel. It's maximum resolution was 1024 X 768 and that was the highest resolution available in the monitors control panel.
Another question bout the 12 inch ibook. because of the smal 12 inch screen i was planning to get an external screen with it, with an higher resolution 1280 x 1024. but is it possible to get that resolution out of your ibook (because that is just a 1024 x 786? so can i change the settings of the ibook?