Hi Dan, that's a tough one, it looks alright. The most common reason this happens is due to floats, it will float weird in a certain browser, shrinking to the point where it looks like it is missing.
I see that the slideshow is floated, but it doesn't look like it needs to be. I would try removing that, also add a clear before and/or after the slideshow, try to make sure it isn't getting floated off.
Another problem could be that it is a tight fit and the slideshow doesn't fit quite right. IE can be picky about this, dropping sidebars and things. The slides are larger than the spot the slideshow is in, and the slideshow is even larger it looks like. Try measuring this area, figure out the exact size and set that slideshow to that size using metadata. Then resize your slide images in an image editor to match that area perfectly and re-upload them. If everything fits just right it might show up.
Take a look at this tutorial on multiple slideshows with different sizes, it might help.