To see some of what I am am talking about visit ChatFX's site. This works in iChat 3 up to the 10.4.10 update. The page I have linked you to shows a changing sample of the options this Add-On has.
Apple added the features used in PhotoBooth and the same floating pallet with forward and backward buttons to display "pages" of Effects and Backdrops.
This pic is from my G4/1Ghz Dual that can only display the Effects and not the Backdrops. To get the Backdrops you have to have an Intel Processor.
Mousing over the arrows expands then to say how many "pages" there are. As default from Apple you have two pages of Effects and two pages of Backdrops.
As you can see here in the second picture there are options to add User Specified items into some of the back drops.
I was using the same camera via a DV converter over firewire to input to my MacBook Pro to get this view. The Number of pages tells you that I have extras added to the default ones from Apple. (I was using an Add-on).
These can be Still pics or Movies.