X11 crashes

[Loki <loki@cs.su.oz.au>]

I'm using Debian kernel 2.2.18 and X11R6 as well
as FVWM 2.something - and X windows hangs quite
often, sometimes 2 or 3 times per day (ok, mostly
not at all, but sometimes a few times in a row).
The mouse cursor freezes, Ctrl-Alt-Del and
Ctrl-Alt-BkSp do nothing.

Question: Is this the fault of X, the kernel,
FVWM, my PS2 mouse, Netscape 4.76, or what?

Any help would be appreciated.

Loki