Go into the Displays panel in System Preferences. Click the color tab and calibrate the screen. Use the Expert settings and follow the instructions. I also have a 20" Alu and the default settings are horrible, but following calibration the colours are rich and there is no noticeable difference in the way the screen appears from top to bottom. Try it and you'll see how much the quality improves.
Bugger about stuff possibly being under the screen though. Not sure what to suggest there...
Did not realize what a poor display I had till after that calibration on my 20" iMac, what a difference!