I understand exactly what your saying, the motherboard does support two monitors, however I believe its up to the drivers to enable that support in XP. For example, I run an office full of dual monitor desktops, and I have 3 different series of Dell Optiplex computers. Depending on which computer, when I boot, I may see two identical screens or just one monitor acitvated until Windows XP is done loading to the login screen.
Now according to Intel - the 950 Graphics Media Accelerator does support two displays on the 945 G Chipset.
http://www.intel.com/products/chipsets/gma950/index.htmSo my suggestion is to not only get the latest 950 GMA driver for the video, but also make sure you get the 945GC chipset driver from Intel as well. They specify that it works with the 945G Express chipset. I don't know if there's much of a difference between that and 945GC but it's worth a try. Install the chipset drivers first and then the video drivers.