So when I'm using an SDL app like Wormux, the screen flickers like the app was in fullscreen to the actual desktop with the SDL window. This doesn't occur on my other PCs, which use Intel Extreme 845G and an ATI Rage 128 Pro. (the ATI card is using the open-source r128 driver, no support from AMD)
SiS graphics cards are well known for their bad support on linux (and in addition to that, they often have a broken VESA BIOS too).
There are some alternative sis graphics drivers that can be found on the internet, both open and closed source, but they often only support the specific or close enough hardware that they were distributed with.