[maroun.c]

Well the D40 is still in production AFAIK the D50 has been discontinued.
Never held a D50 but I guess the D40 would be more compact.
The D50 will autofocus with more lenses and is famous for low noise performance at high ISO.
The D50 70 70s 80 200 and 300 all have a built in motor to autofocus with lenses that do not have a built in motor (non AFS)
Tough choice for sure and lense choice would be even harder as you can switch bodies every few years but you are stuck with your lenses for longer time.
Reefman
the 18-200 is not professional grade.
It does have a metal mount but infortunately is made of less resistant plastic than other pro lenses.It is better built than the other kit lenses though.
mine broke open after falling from around 45 cm, many other users suffered with it braking after minor falls. also it is reported to be just a bit soft wide open and at the edges and suffers from distortions at the wide side. all 18-200Vr do or will creep from 30-120mm for some this is a major no no for others including me it not that serious.
Still it is a very capable lens and does provide very nice pictures if used correctly. it's main advantage is in being a one lens solution. VR is just great and the difference is really clear when one assesses the percentage of blurred shots when using a non VR lens.