Re: 9800GTX+ crashing, hardware or software?
Well I've been using 180.* drivers from experimental and unstable (which recently leapfrogged experimental for nvidia) and still been getting the crashes, so the bad news is that if you do manage to install the "unstable" driver I don't think it will fix your problem.
To install sid drivers on lenny, add the sid/unstable repositories to /etc/apt/sources.list and run "apt-get -t unstable nvidia-glx". I don't know whether it will succeed, but it should automatically update anything it needs to work with the newer version.
It isn't just OpenGL either, something about scrolling an ordinary window sometimes triggers it for me.