I am totaly new with Linux (at the Moment using Ubuntu 7.04), so i found it really difficult to do that. So...I found in the Internet how exactly to install Nvidia .run Drivers. After "extracting" the package it said that i have to stop the X. I looked among different Forums and found that i have to run at runlevel 3. So I looked how to change the current runlevel - and found this solution

"su - init 3"

well, no success. I changed the "su" with "sudo" and when i pressed enter nothing happened.
My question is how to run at runlevel 3 in order to install my drvier?
I would be very happy if you could give me a very detailed howto (step by step) because i am a real noob
Thank you in advance!

To shut down X sever you should press Ctrl+Alt+Backspace. Switching to runlevel 3 have nothing to do with X.

Ok. Thanks for the info but than still - how to get into runlevel 3 in order to install the driver?

What they're saying is that it's X server that stops you being able to install the drivers, not the run level

If you really want to do it from run level 3, change the default in /etc/inittab and reboot