Wolfgang Mueller
Following your advise, I found a size of 1024x768 in "Size & Orientation". The tool gives me the choice between this value and "Disabled", but 1600x900 is not available. So I selected "Disabled" (whatever that means), but that did not help. After closing the tool and recalling it, the old value of 1024x768 appeared again.
You have been bitten by the same KMS bug as I did. Please see this post:
http://linux.derkeiler.com/Mailing-Lists/SuSE/2011-04/msg00431.html
So far the only solution I can find (tried configuring X manually) is to
use xrandr to add and set the mode. Your should:
1. Run:
,----
| hwinfo --monitor | grep 1600x900@
`----
to find the Hz that that mode runs at.
2. Generate a modeline with cvt:
,----
| cvt 1600 900