There's always the -core option on Xserver, but the guy a couple posts back reported no luck with that. I imagine that the /var/log/XFree86.0.log would have something usefull in it if you turn of [gxk]dm so that it doesn't get overwritten. I can't do that unfortunately. I've been having this crash problem for several revisions now, so i'm not hedging my bets as to a fix.
Can you make it crash consistently? I can't, though its seems like playing videos and logging out of gnome or kde are more likely to make in crash than, say, opening up a couple of xterms.