The waterfall uses a matrix in the image map node.  A matrix has all your animation images composited in rows and columns, like a post office's pigeonholes.

     Math nodes manipulate the frame number to decide which "pigeonhole" cell of the matrix to display at a given moment.  The nodework might look intimidating, but you could simply copy my material to your own project, and replace my matrix image with your own.  If your matrix has a different number of rows/columns, just adjust the numbers (circled) to match.

     I've overlaid a reduced-size copy of the matrix onto a blank area of the material room screenshot so that you can see what one looks like.  Notice that you only see one cell image in the Poser material preview.  If you advanced the timeline to the next frame, that image will change, automatically.

     While it looks more complicated -well, it is more complicated- to use a matrix, the matrix has the advantage of being universally robust.  Even in versions of Poser which have issues reading the movie node, the matrix works.  Even if rendering in network in 64bit (or a mixed group of 32bit and 64bit), the matrix works.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5