Other than tt, If you are getting the D40, I think u cant use the 50mm f1.8.
Since its at 50mm, if you are taking pictures for a group. Eg. 8 ppl side by side..
you may have to start say.. 4-5m away. Tt's its quite far away... and it looks quite foolish to ppl who do not know wat is the contrain. Furthermore, at times, u might be restrained by space.
50mm is a lens with a fixed focal length.. means u have to move urself instead of the lens.
It requires some discipline in a sense.
Hope this explains.