Hey notaFish,
I have come across myself, I suspect its a bug in the rendering engine of IE for handling animated opacity on alpha-transparent pngs
In my non expert kinda way of trying to explain it
Your using alpha transparent pngs which work fine in modern browsers and also lower versions of IE with various png fixes. however! from my experience ie cant handle changes to the opacity of the alpha value of image during transitions. thus why your getting the black outlines.
to highlight it, looking at your page in IE your main png areas are alpha transparent images and I picks up the opacity correctly from the image file on load, as the opacity value of the alpha png is animated IE looses the default alpha level in the image, and tries to handle it based on absolute values. hence the solid black lines.
To the best of my knowledge there is no real fix for this, the only solution I managed to find that worked better, if my memory serves me well was to use png8, and specifying the matte as the background colour, although I dont think this is going to be a solution for you due to the patterned bg.
here is the original post....
http://www.designforums.co.uk/web-coding-development/5490-png-problem.html
The final solution I developed for the above problem was to serve flash for IE only browsers.
used here
Web Development | Mobile Applications | SEO | Web Ecommerce - Ventutec in the main animation on the homepage.
FF, SAF etc use JS, IE uses flash.
An alternative solution is you don't animate the opacity values of your alpha transparent png in IE.
Ps. Other larger devs are having this problem too.
view in ie and hover over the download button/icon/link
http://www.panic.com/coda/
Hope this helps.