I have the same on-board video chipset. It will hang for any screen saver requiring 3D video acceleration. To avoid it, I just picked "blank screen" as my screen saver. I power off my monitor will idle, so the screen saver doesn't matter to me.
I never found the root cause of the problem, but linux support of via is not as good as with nvidia video. If you get an Nvidia video card, you can get 3D video acceleration.
You can also probably avoid freezing by switing the video driver from "via" to "vesa". Do
sudo nano /etc/X11/xorg.conf
scroll down until you see:
Identifier "Generic Video Card"
and change "via" to "vesa" and save changes. The change will take effect by rebooting, or restarting X with ctrl+alt+backspace. The vesa driver shouldn't hang the computer, but it doesn't offer 3D video acceleration either. If you use vesa, you can't watch full screen video, but you can with via.