Image saving

I just loaded Photoshop 7.0 onto my new computer with Win XP Home. I tried saving an image from the internet as a .bmp file. In the saved image's properties, it says its a .jpg. And when I try to open it in Photoshop I only get this error message:

Could not open "filename" because an unknown or invalid JPEG marker type is found.

Can someone help??? (Sorry for x-posting.)