He's asking what type of file. The extension is what's at the end of the file (animal
.jpg - .jpg is the extension). If works refuses to open it, it's probably a .pps or something with macros enabled, which do pose a security risk.
If you are sure your source is good, (and it's a .pps, or power point slideshow), then you can save the attachment to your hard drive, then open it with power point, or use the free viewer if you don't have that installed.
http://www.microsoft.com/downloads/d...displaylang=en