I looked at this again in IE6 and there are a couple of small problems.
your using the iefixpng.htc aren’t you?
you have your image on fine, but a coule of your images are not background images, and I think that is the problem with this htc file, it seems to want your images to be background images.
so the pic with the 2 women and the bottom images have a sort of non image above the image. I currently can’t fix this as I am looking for a solution myself for my site for IE6, as I use the iefixpng.htc file thing
the centering of the site can be done quite easily, if your using tables then center it, if your using divs then I done it on one site using margin-left:auto; and margin-right:auto; in the css for body and css for my wrapper div and adding text-align:center for both, not sure why but IE seemed to like the text align center for centering the images.
About the centering thing: Horizontal wasn’t my problem, but vertical.
Tried various solutions and all had some kinde of problem. It took to much time to figure this one out, so i stepped away from it.