Slow screen refresh in Windows

[RGould8 at aol.com]

I did some digging around in the archives, and I see that some folks are 
having this same problem, but in my case, I haven't read a solution:

I need to be able to click on a button, and have an image "shrink", 
width-wise, until the width is zero and the image disappears:

repeat with x = 300 down to 0 step -10
    set the width of image "screenshot" to x
    set the loc of image "screenshot" to 300,300
end repeat


This code works perfectly on a Mac, but in Windows, I get a watch-icon for 2 
seconds, and then the image chuggs and chuggs until it disappears.   The 
performance is much much worse in Windows.

I've tried putting an unlock screen in the loop, and I've tried the "wait 0 
with message" technique.   What other way is there to accomplish this effect 
and make it work smoothly in Windows?   The image is nothing special - - - just 
a small 300x 150 BMP file.