Building Animation Clips
To add animations to your command briefings, all you need to do is to create a directory under your 'data' directory call 'Interface'.   Once you've stored the ANI file there, it will be available from FRED.

You can convert AVI files to ANI files by using a tool called AC.EXE released by Adam Pletcher of Volition and available on the Descent: FreeSpace Developer's Network.   Also included inside of AC.EXE, is a program that strings .PCX files together into an ANI.

Heiko Herrmann has written Descent Manager VPView32, which is viewer program that allow you to see, hear, view, and extract all of the data in the VP files.  Heiko also runs the Descent: FreeSpace Developer's Network, which is an excellent resource.