I know this is an old post but it's still relevant as the original problem was not really addressed completely. I can't address it completely either but I can add my experience using VIA/S3G UniChrome Pro II IGP built into a netbook computer.
I currently have XP running on my Sylvania netbook. XP reports that the above chip type is installed. XP also reports that the following modes are valid: (640x480), (800x480), (800x600), (1000x600) and (1024x768). All modes support 256, 16bit and 32bit color modes @60Hz. In addition to the small internal display, the chip supports an external display at the same time.
I've tried unsuccessfully to install any Linux distro onto the netbook that will support any graphics mode above 640x480. PCLinuxOS 2010 recognizes the chip somewhat but defaults to (640x400). This is not a usable resolution for Linux IMO. Through the PCLinuxOS Control Center I was able to set the "Resolution" setting to "Automatic(16bbp or 24bbp)". This allowed the resolution to be increased to (640x480). I can do this for the following Control Center graphic card settings: Chrome9-based card, S3/UniChrome-based cards with 3d support and VESA. There is nothing I can do through "Configure Your Desktop" display settings that changes the resolutions to something above (640x480). My 2 cents.
http://unichrome.sourceforge.net/ is the only site I found that might have a driver to support the higher resolution modes but I'm not sufficiently knowledgeable to compile, install and test their driver. Perhaps someone else can help with this.