Do you have 3d support? Try running this command in the terminal:
Are you running Yast while in text mode? If not, try that. From the terminal type su, enter root password and then init 3. Log in as root and then run sax2 -r -m 0=nvidia. If that fails run sax2 -r -m 0=nv
If you have a driver CD for your monitor, you can use that while you are in Yast / Monitor / Change/ Utility Disc. This way, Yast will have the inf file for your monitor and know what resolutions and refresh rates are supported. If you do not have the disc, you can download the driver from the Samsung site and burn it to a CD.
Definitely install the Nvidia driver, that will give you the best chance of being able to set the proper resolution.
Finally, confirm what resolution you are actually running using your monitor’s info menu. I thought my monitor was running 1024 x 768 (I wanted 1280 x 1024) because of the large fonts it was using. I fought it for about 30 minutes until I checked the resolution on my monitor and it actually was 1280 x 1024, but I was fooled by the big fonts.