Slackware :: (ver. 13.37) After Delay, New User Causes X To Crash?

I have a new installation of Slackware 13.37 on an old Dell Optiplex P4. Right after installation (when I only had a root account) I found that X (regardless of window manager) would develop video problems after a few minutes (horizontal lines, slowdown -- though without crashing). A message board informed me that that there was a bug in my onboard Intel video chip that would require me to enable shadow buffering (which amounts to disabling 2D acceleration). I made the change in the Xorg.conf, and the issue disappeared.

However, once I finally got around to adding a new user, X began acting up again, though I have no idea whether it's related to the earlier problem. Now, after a few minutes, it actually crashes -- though only when started under the new user. Root still works fine. I'm new to Linux, and still trying to sort through all the different logging tools, so I'm not sure what I ought to be posting. Here's the relevant bit from Xorg.0.log:

Code:
[ 1886.178] (II) intel(0): Modeline "800x600"x70.0 45.50 800 840 920 1040 600 601 604 625 -hsync +vsync (43.8 kHz)
[ 3090.195]
Backtrace:
[ 3090.195] 0: /usr/bin/X (xorg_backtrace+0x3b) [0x80e72fb]
[ 3090.195] 1: /usr/bin/X (0x8048000+0x5dbf5) [0x80a5bf5]

[Code]...