Since you are running Debian, you'll have to use the tarballs, they're as easy to install as the rpms.
I don't even think you need to change your runlevel, at least I never did with Debian. Then again, I think runlevels 1-5 are all equal in Debian, you configure them yourself.
The only differences between RPM and tarballs are:
1. Download the two source tarballs (kernel and GLX)
2. Untar them
3. Su - (to get root privileges)
4. Cd to each of the directories created and make install in both.
5. Add NVDriver to /etc/modules, to load the kernel module at boot time
6. Change the XF86Config file, like Itzac said.
7. Also add 'Load "glx"' to the Module section (these are the opengl drivers, but they won't do any harm)
8. Restart the X server and enjoy
