IE's Default

I'm using a binary stream to send down a file from the web server. I've been having trouble with IE and getting it to recognize my file. I've added the filename as a paramater(?filename=file.jpgw) to handle IE's mime type mangling, but I'm still having trouble with IE's default Save As Type being HTML. When we send down a jpgw (geo-jpeg) file IE wants to save it as an HTML file. I've got the correct filename showing in the Filename box, and if I choose the All Files option from the Save As Type drop down then the file is saved with the correct extension. I'd like to have the All Files option choosen by default. I know it's just a couple of clicks but we have some noivce users that can't seem to get that