[iwantanimac]

Did you read the WPS creation page on Rockbox.org? The custom tags for albumart and such are missing, but for basic WPS creation, it is a good guide.

The code you're after looks like this:

%t4[Image 1];%t3[Image 2];%t3 [Image 3]

Basic rundown:

   ;  : Split items on a line into separate sublines
  %t  : Set the subline display time. The '%t' is followed by either integer
        seconds (%t5), or seconds and tenths of a second (%t3.5).

So, you set it to display each image in it's own subline with a delay between each, and hey presto, animation!

All of this is available on the page i linked above.

Hope that helps you out!