Resize circles with drop shadow

i have several circles on my site with a drop shadow (created in Photoshop and saved as PNG’s)…the circles are actually part of the menu…once u select a circle, the circles resize and become smaller…

my problem is that when I resize the circles, the quality of the circles becomes horrible…

How do you resize a shape with a drop shadow without losing its quality? if i try to make a drop shadow in flash, it doesnt look as good as the drop shadow in photoshop.

please help…thanks!