different implementation with yast and SaX?

I first used SaX2 to configure my X11 environment, the current resolution is too high and the screen flickers. SaX2 recognize my card instantly(ATI rage Pro with 32M), but it cannot configure it under 1024*768 with 85Hz . so I tried yast, it get all of these working and wrote to the configuration files successfully. Why is that? Cheers Liu