make a few larger background copies and duplicate them all
then for each frame, show 2 backgrounds, 1/2 the loop length apart.
Fade the top bg layer out from 100% to 0% over the length of the loop.
or something like that!

(
Bloop Fri 16 Jul, 22:10,
Thu 31 Jul 2008, 15:06,
archived)
Hurry . . .
there's no end to it !
(
Valin I changed glasses while I wasn't looking,
Thu 31 Jul 2008, 15:13,
archived)