I have a custom image in the header on my site, http://canadafoosball.wordpress.com . It shows up perfectly well in Firefox and Chrome, but Internet Explorer just shows a broken link where the image should be. Any idea why this would be happening or how to fix it? Any help would be greatly appreciated.
That is because it is save in CMYK colorspace. Images for the web have to be sRGB (not Adobe RGB either). All browsers but Internet Explorer will display CMYK images.
You need to save the image in sRGB and upload that image.