When you download a new kernel, it would be best to make sure that you have the latest nVidia drivers already downloaded (not necessarily installed, just downloaded to your nvidia folder).
You'll have to reboot and at some point you'll see the screen go blank. You may get a flashing cursor in the upper left corner, and you may even get some rapidly flashing text in the upper left corner, but regardless the screen will be substantially blank.
When that happens, just hit CTRL-ALT-F2. That will switch you to you second virtual terminal, and you'll see the login prompt (it'll say something like 'localhost login:'). That's your terminal login screen. Just enter 'root' (without the quotes). It will ask you for the password; give it your root password.
At that point, the scripts I set up will kick off and automatically compile and install the drivers and reboot the machine, whereupon you will come back up with your graphical interface again.
If that doesn't work, you're screwed.
