You know what's really strange. I desided to double check your blog so I cleaned out my cache while sitting here with an open window where you blog was loaded.
the blog stayed but the header picture disappeared without me doing anything. But the blog stayed. Strange...
I'm not sure what's going on. IE 6 is trying to convert it to a *.bmp when I save it. At about 300kb in size.
I went ahead and loaded the header into Paint Shop Pro and exported them out as a *.png and a *.jpg. I know that there are file extention restrictions on the header uploads. I'd try the *png one first but I have a feeling that you might have to use the *.jpg one:
The *.png is 88kb and the *.jpg is 17kb.
See how they look.