I'm guessing you are using a POP account from your ISP instead of hotmail. If you are using hotmail in Windows Live Mail, you don't need to worry about backing up the emails as they'll be downloaded automatically when you reinstall it. However if you are using an account from your ISP, you'll need to back them up. In Windows Live Mail, go to File > Export. The rest should be simple enough to figure out. Then after you reinstall Windows Live Mail, just go to File > Import. (If the File menu doesn't show, press Alt on the keyboard.)