It's solved! I'm running Debian Testing, and i've got 1280x800_85 Hz! You have to download driver Mageia Cauldron for i586 from http://rpmfind.net/linux/rpm2html/search.php?query=x11-driver-video-sisimedia . Then, following this article http://www.howtoforge.com/converting_rpm_to_deb_with_alien , you'll convert that .rpm to .deb and install it. It works!!!