The 18-55 IS is a fantastic lens for the cost.
I would strongly recommend that you get that as your first starter lens.
Use it for a few months and then figure out yourself (by all means take some advice) what you need.
Sharpness is only one factor of many, but it is the one that beginners get all obsessive about.
If you cannot get stunning images from the 450D/40D + 18-55 IS the reason is behind the camera, not in front of it. :-)