I did a search, and while there are many similar issues, there are just as many varied solutions, and I'm having trouble figuring out which one is specific to my issue as it's not quite the same as the others.
The website is http://www.thewildflowergroup.com/
I'm having trouble with PNG alpha transparencies in IE8 as well, but I'm not seeing black splotches or artifacts around the edges. The backgrounds of the PNGs at top are just solid white. I'm using the IE9.js version found here http://code.google.com/p/ie7-js/ to deal transparencies, and it seems to be working on other pages. But for that top section, I'm also using Jquery Cycle.
I've wrapped the images in divs, hoping that by fading the divs, the images would go back to being transparent, but no love. Any advice?