http://www.nikonchat.com/nikkor-d40x/

Is there a faster lens i can buy for my nikon d40x?
Currently i have a Nikon 18-55mm f/3.5-5.6G ED II AF-S DX Nikkor Zoom Lens. Can i buy a faster lense or is the speed based on the body?
I probably didn’t make this clear. But what i mean is that i want a lense that can auto focus faster than what i have now.
Probably not so much that you would notice. Autofocus is directed by the camera’s electronics. The brain in the camera is telling the lens what to do. It is possible that some lenses might be capable of moving where the camera has told it to move faster but I doubt it would be enough for you to notice.
If you in dark low light situations then a faster f-stop lens would be able to focus where your current lens can’t, but then getting a add-on nikon flash would give your camera better focus assist light which would do the same thing.
Iceland seen trough my nikon d40x