How do I change the way a .pps file looks on my page?

I'd like to change the way the "icon" appears on my website for a .pps file I've loaded.

Right now it just shows as a white page with the upper corner turned over (I'm sure you've seen that before) and the file size is also displayed beside it.

Does anyone know how I can have an image displayed instead, and use it as a link to open the file? I haven't found any reference to this kind of thing in the help files so don't know if it's possible, but I really need to know how to change the ugly appearance it has right now.

Thanks.