Mac Mail animation issue

[swf]

For quite some time I have been having an issue with Mail. There are 3 Macs in the house, 2 Macbooks (both running 10.6.8) and an elderly iMac G4 (10.4.11). When I receive the occasional animated greeting card or some other animated content (e.g. falling leaves in an autumn scene or a wagging dog tail), the motion does not appear on the Macbooks, but DOES work on the ancient iMac. Any idea as to why it doesn't function on the newer machines with a more modern OS? Any possible solutions?

[Ken Sp.]

Are you sure you have current Adobe flash and Flip4Mac installed?

[swf]

Ken, all are up to date. The Macbooks are much more current than I can get for 10.4.11 on the iMac. Yet the animation works on the old machine, but not on the newer ones. Strange!