One of my machines has a 845G chip (82845G/GL) and it used to freeze from time to time on FreeBSD: no way to terminate X, no remote access using ssh, nothing of interest in the logs (actually, no logging after the freeze).
I tried the older XAA but it was the same. I disabled acceleration and never experienced any freezes since then.
Code:
Option "AIGLX" "FALSE"
Option "NoAccel" "TRUE"
HTH.