you'll need to download the drivers for your nvidia if you want you r card to work fully (otherwise no accelerated 3D graphics), these are available from
http://www.nvidia.com/object/linux.html.
Follow the readme for installation, though all it amounts to is installing drivers then changing a line in your xf86config.
As for your keyboard problems I presume your using the wrong keyboard map, look in /etc/X11/XF86Config and edit line:
Code:
Option "XkbLayout" "en_US" # or "es" or any other
changing "en_US" to "gr" (I think, since your greek you'll require a greek layout)