Something is amiss somewhere. I've been using this driver on 2.6.34 (from kernel.org) for a few weeks now. The kernel module built (and still builds) without fuss, and performance is excellent on my GT240.
I have this script at boot-time to rebuild the module for me, in case I reconfigure/recompile the kernel:
$INSTALLER --no-network --kernel-name=$KVER --no-x-check --kernel-module-only --ui=none --no-questions --accept-license
What does your system show when you type this command:
/bin/ls -aF /lib/modules/2.6.34/build/include/*