How to fix a blurry screens

When installing my Acer 19'' (AL1916W) on my wife computer as a dual screen, I noticed that the text wa blurry on both screens (both the same). I have updated the video card driver (a 7800GS AGP) but some areas where still not right.

Then, I pressed the Auto button on both screen and I saw an improvement. So, I decided to open full screen a document containing text on both screen and press again the Auto button: Problem fixed !! I was quite simple but it took me 45 minutes to solve it properly.

This is a picture of the video card, using AGP technology:
And this is the set