How to preserve jpg pict quality when flash movie exported in %

I´ve experienced some distortion with .jpg pictures on a flash movie exported in percentage ;
I expected that there would be some difference when visualized with different resolutions and monitors , but not too much ;
is there a way to mantain pictures quality at last in the most common resolutions (800x600 1064 x 768) ? what do you do when export your mc in %age ?

(all Picts have been perfectly tunned for the web by Macromedia Fireworks)

Cheers