如何配置IE7以下载文件类型而不是在浏览器中打开

I have written a watir script that downloads files. One of the files it downloads has a .dcf extension. Months ago, on my machine, I changed a setting somewhere so that .dcf files prompt for download ("Do you want to open or save this file?") instead of opening in the browser. This is the behavior that I desire. I am using XP Pro/IE7.I have written a watir script that downloads fi