KUbuntu-specific version of TPG's directions.
Ctrl+Alt+F1 to switch to console one. Log in.
sudo /etc/init.d/kdm stop
stops the X server.
chmod +x NVIDIA<press tab to complete>
./NVIDIA<press tab to complete>
launches the install. At the end it will ask if you want to automagically update your xorg.conf file. Tell it yes.
sudo /etc/init.d/kdm start
Starts the X server again, this time with 3D acceleration.