Presently, the nVidia driver support in KernelCheck Lumen is broken. This is because you can't actually run the nVidia install package with X running. In order to install the latest nVidia drivers using the nVidia install package, you must do it in "runlevel 3" (shell without X running).
If you are currently using nVidia drivers with your current kernel, it is recommended that you select the option "Reconfigure the X Server" in KernelCheck. This will force X to load a fail safe driver (usually the "nv" driver). Doing this will make sure X will load after you reboot (it will crash otherwise).
After you have rebooted and X has loaded, you should be able to install the current stable nvidia drivers using the "Hardware Drivers" applet in Gnome (System -> Administration -> Hardware Drivers).