Yes, the infamous GMA 3100--notorious for sucking ass as a GPU (in some instances, it can even behave as a graphics decellerator, giving worse performance in video apps than CPU-only decoding).
One thing that you might try is enabling QuartzGL (search the tubes for the 'Quartz Debug.app' force-quit procedure). It may sound crazy, as this often caused graphical anomalies in 10.4 and 10.5, but it helped smooth the glitchy graphics on a system of mine with an old GMA 950. However, if you opt for this solution, it is important to selectively disable QuartzGL for the Dashboard app. In order to do this, you need to add a parameter to the Info.plist of Dashboard.app. So open the Dashboard.app enclosing folder, then Info.plist, click "Add Sibling;" then rename the new parameter "QuartzGLEnable," switch the type to boolean and set the value to "No."