Not sure what you mean but here is some info.

If your .avi is originally at 25 fps, then the animation you are making must have the setting of 25 fps under the make movie options, then the .avi will play back at the correct speed.

The surface that you are going to use the .avi on must be as close to the aspect ratio of your .avi as possible. If your .avi is 4:3 (TV aspect ratio), then try to get the screen size of your model to also be roughly 4:3 in ratio of size.

When mapping the screen, use planar mapping in UV Mapper and select "don't split". That way your avi only renders on one surface.

If you were asking how to apply .avi:
At diffuse colour, select new node, image map, movie, and browse to find your .avi. It is best to use uncompressed .avi for textures. Even though the file size is large, it is the best. Compressed .avi can cause some funny effects. But maybe that's just me.