I called Apple today and went through the problems that I'm having with the Windows distortion. Also provided them with some snap shots.
Last night after using iPhoto, the problem appeared again and started showing up indiscriminately in various windows. Funny thing is that not all windows were effected, even in the same program.
I've set up an iWeb page for anyone is interested in the screen shots that I have managed to take. Two options, if you have dial up use the Photos Page (Snap Shots) Broadband use the direct links at the bottom of the page for full size screen shots (23" Display).
http://web.mac.com/dworld/iWeb/Site/Mac%20Mini%20Graphics.html
Meanwhile Apple suggested that I start off the process by doing a Hardware test. Since tomorrow is a Public Holiday in Ozz I'll do it tomorrow night and then get back to Apple. Pretty sure though that it's a Software problem and not hardware.