Malcom,

It seems you got it worked out, so this might be late but here's what I
learned dealing with Flash and images.

I found using Fireworks to sharpen the images works wonders, and is a little
better than PS's un-sharp mask. Your images seem a bit blurry, compared to
what I imagine the originals are, Also, as you mentioned, Flash doesn't like
decimals. It also doesn't like 100% Alpha channel on images, at least in
tweens, so I always use 99% instead. I get no shift or "weirdness" with them.
Granted they are not sysmbols, except for the thumbnails, but I think it hwelps.

Good luck.

Alexis