CoreImage and CoreVideo, as far as I understand, will scale to whatever processor it's running on.
"The performance gains and features supported by Core Image ultimately depend on the graphics card. Graphics cards capable of pixel-level programming deliver the best performance. But Core Image automatically scales as appropriate for systems with older graphics cards, for compatibility with any Tiger-compatible Mac."
http://www.apple.com/macosx/tiger/core.html
Sounds like it's optimized for certain graphics cards (which are listed on that page) but it will scale back for older graphics cards.
The wording on that page leads me to believe that no one with a Tiger-compatible machine will be left out in the cold concerning CoreImage/Video.
Bascially, CoreImage and CoreVideo implement common filters and effects for images and video and process those routines with the graphic card's GPU instead of the system processor, resulting in much better image and video effects and quality. In essence, it'll make images and video faster, since your computer's processor won't have to do much of the work concerning image and video manipulation -- instead, the graphics card will do much of it. The better your graphics card, the better improvement you'll experience with CoreImage- and CoreVideo-enabled applications. If your graphics card doesn't meet the requirements, CoreImage and CoreVideo applications and routines will still work, but you won't get the benefit of the improved quality and speed.
Think of it like Quartz Extreme for images, video and applications, except
everyone gets the spinning-cube-fast-user-switching effect.