The Basic Configuration

First of all, Lets try to get rid of some Lag. There is nothing as frustrating as Lag when it comes to playing games. So unless you have a very powerful system I suggest you turn off the shadow settings since the difference is barely noticable and you gain a good deal of FPS by turning it off. Adjust the other settings if needed for better performance.
Call of Duty 4 is a great looking game but that pales in comparison to the game play it has to offer. So adjust the setting for the best performance.

I will not teach you what button is used to move,run and shoot (learn that yourself) but you can adjust the keyboard layout and mouse settings to your liking. If you have a spare button in your mouse that you can easily access then I suggest you add your "melee attack" button there for quick access to knife the enemy if ever you bump into each other. Also designate a mouse button for your grenades because you will be spamming them a lot.
I use a Logitech MX518 mouse and put my "melee" attack" on my BACK thumb button and my "push to talk" on my FORWARD thumb button and my 'throw frag grenade" on my MOUSE 3 button.