So I know this has been posted about a billion times to other blogs. But I figured I might as well make my blog complete by telling you how to add your own icons (or change icons) that appear inside SharePoint for specific files.
The icon that I wanted to add was the movie icon for .mpg and .mpeg files. I simply opened up a folder in Windows Explorer and took a screen shot. Then I used my favourite simple picture editor (mspaint.exe) to strip out just the icon in question
Finally, I saved it up on the server under:%program files%\Common Files\Microsoft Shared\web server extensions\60\template\images as icmpeg.gif, which seems to be the convention for SharePoint.
The next step is to crack open the \template\xml\docicon.xml file in my favourite simple text editor (notepad.exe). I made a copy of this file first incase I screwed anything up. Then I searched for
Finally, I opened a run window and reset IIS using the command iisreset. Refreshing SharePoint caused the icon to show up immediately.
I can't take all the credit on this one, LauraJ had some good advice (and quite possibly some more information, if you get lost).
Icons are cool!