This is an effect called Aliasing and you will hear it more when referred to the method to get rid of the effect which is called Antialiasing. If you want to know more about this stuff then read my tut on the technical side of images.
Specifically post #9 & #10 in that thread.
Unlike the text in #9 & #10 tho you have the high res information in the image but the zoom out with the software your using is whats causing the issue so its more of a fault with the software than your work. I use an old version of PSP and it does this for me too. Its very common and not taken into account by most software writers.
Last edited by Redrobes; 06-20-2010 at 08:37 PM.
Thank you! I'll give it a look.