When talking about interleaved and PlanarImageFormat the main difference is how they are store in memory.
Interleaved images have all color components needed to represent a pixel placed at the same place in memory.
Some examples of interleaved formats are RGB24, RGB32, YUY2.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwmt/html/YUVFormats.asp
$Date: 2006/11/24 18:21:26 $
Original version of this document at http://www.avisynth.org/InterleavedImageFormat