The 18-55 II was announced as the new entry level kit lens when the D40 was introduced. On Nikon's site, the 2 versions seem to have the same optical design but slightly different exterior. The technical tests performed by photozone.de show that the new version has better overall resolution but very slightly worse CA. It could be sample variation, it could be something else....
I got f4 at 55 mm on the 55-200 VR

(not to mention the VR...)
Darrin
P.S. The D40 has a focus assist lamp which helps with autofocus in low light...