Comment 4 for bug 152139

855GM hardware is known to hit problems which aren't yet cured in the updates.

The latest un-released patches I've been working on to cure the crash is in this deb:
http://www2.eng.cam.ac.uk/~pcjc2/ubuntu/xserver-xorg-video-intel_2.1.1-0ubuntu10~pcjc2_i386.deb

However there are still corruptions to the display seen after resume with compositing enabled.

The addind a second monitor fix sounds to me like like you need the above package.