Oh... I thought you had tried it with the kernel module loaded, and it still didn't work.
OK, that's an entirely different problem then.
Debian uses one of either /etc/rc.modules, or /etc/modules, or some file similar to that. It's either a list of kernel modules to load (if it's that, then just add "nvidia" to that list somewhere), or it's a sequence of /sbin/modprobe <kernel module>
command (if it's that, then add /sbin/modprobe nvidia
That'll load it on every boot.