Ubuntu :: 9.04. Crashes To "switch User" Screen When Playing Video?

When playing a video file, the system suddenly "crashes" and loads the switch user screen, as if I had selected a different user in the switch user/shutdown panel at the top right of the screen. This seems to most commonly occur with .mp4 files, but also occurs with .avi. I have gotten this problem while playing videos in Totem Movie Player, VLC, and Banshee. My system has 4GB of Ram and Intel Dual Core T4200 processor (2.00 Ghz).

lspci returns the following:

00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)
00:02.1 Display controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)

A simple integrated card, but should be enough for watching videos. Perhaps a driver upgrade is what I need.