D2 is a game designed for old 4:3 aspect ratio screens so when you push the maximize button the games stretches it's window to the largest 4:3 window your resolution does support. Works great if you got a 4:3 screen but with a widescreen display the screen is not entirly filled to keep the 4:3 aspect ratio to prevent grafics distortions.
Now patch 1.13c added switch "-nofixaspect" which allows you full stretchability ;-) of the window. But be warned before using it: the window will be in fact only stretched while the 4:3 ratio of the game remains! Thus maximizing the window with the -nofixaspect switch on a widescreen will result in grafics distortion.
Just wanted to say thanks for taking the time to help me!