emoticons show up in FF but not IE

My new blog at https://www.beerdata.org is working like a charm except for one little detail. When I look at the site with Firefox I can see and click on the emoticon options for user comments. But when I look at the site with Internet Explorer all I see is a series of ‘x’ marks like the images are broken or missing. Any idea as to why this may be happening?

I’m using Firefox 1.0.7 and Internet Explorer 6