What exactly did you do? What do you mean by running xf86config?
I haven't tried installing the nvidia drivers under debian, but I have on quite a few other distros. This is what I do.
1.) I download the current nvidia driver
2.) I exit the x window, I have a round about way of doing this but this is the way I prefer.
I change the default runlevel to 3.
Then I reboot.
Then I cd into the directory that I placed the nvidia package in.
Then I run the nvidia package
Then I EDIT my xf86 file.
I change nv or vesa under the monitor section (I believe) to nvidia
Then I startx