Hi,
Is this a laptop?
I would start with the latest drivers from SiS's web site. They are stable. Download them here:
http://www.sis.com/download/download_step1.php
You must install the drivers in Safe Mode. Otherwise they won't install at all.
When in Display Properties, go to the Settings tab and click Advanced... Go to the SiS Utility Manager tab and click Driver Mode Settings. Try selecting the resolution from there. Be sure not to exceed the max refresh rate your monitor can handle. To be safe, use 60 Hz.