dark pictures from Nikon D-70

Dear forumvisitors,

I recently bought a Nikon D70 with the standardd AF-S 18-70 lense. I met a
problem, which will often have been discussed here before. With all
programms (auto, P,S, A) the pictures seem to be too dark. By using more
light between 0,3 to 2 stop, one can improve somewhat.
But even then I have to use the option Enhance within the programm
Pictureproject to get an acceptable printable result.
Should I solve this problem by using Photoshop or has this problem to do
with the choosen settings or with the camera itself? I am a newbie with
digital photographing. The photograph is much clearer on my 18 inch Iiyama
TFT-monitorscherm than on my 19 inch Iiyama RGB-monitor, even so with
printing the picture is still to dark.
I put three different uncorrected photograph shots of my Nikon D70 on my
homepage. They contain also detailed information about the used settings.

Picture 1: see http://home.tiscali.nl/hzwartjes/download/foto1.JPG
Picture 2: see http://home.tiscali.nl/hzwartjes/download/foto2.JPG
Picture 3: see http://home.tiscali.nl/hzwartjes/download/foto3.JPG

Which Nikon (D70) user can help me out? Thanks anyway

Eric