OK... this worked up until yesterday! I had 2.6.1 running with a minon.de patched version of the 53XX driver and it was all fine. Had to reboot yesterday for something and boom, suddenly X wouldn't start. If I commented "load glx" out of XF86Config-4 I had "failed to load GLX", if I left it in I had "Initialisng GLX" followed by being dumped back to the console with no other error messages.
Googling around made me suspicious about the TLS libraries, plus the only big change that had happened in the period when it stopped working was an apt-get dist-upgrade, so I followed these instructions
to build a proper Debian kernel, based around the 4496 nVidia drivers. This seems to have worked, and this time the TLS libraries have been installed. I have verifed that both the kernel module and GLX libraries are the downgraded version; I initially installed just the kernel module, and starting X threw an error about mismatched driver versions. Installing the nvidia-glx debian package cleared this error, so I imagine the GLX library is now the right version.
Now, when I start X, I get "failed to initialise GLX" regardless of whether "load GLX" is in the XFConfig-4 or not. This is rather frustrating. I don't particularly care about 3d acceleration, I just want it to work, but I'm not even all that sure about how to get more information on what is wrong. I'm about to turn my second monitor off and revert back the open source nv driver instead, but obviously I'd like my TwinView back. Can anyone make any suggestions?