As I've mentioned in posts before where you asked about programs... if your computer is so old that it can't run anything newer than 10.5.8 your going to have hardware limitations that will become considerably annoying working in almost any program.
If your looking for 3D Modeling/Animation you'll want to have a look at things like Cinema 4D, Autodesk Maya, Autodesk 3DS Max.
If your looking for specifically 2D Animation I'd have a look at Adobe Flash or Adobe After Effects.. most animators in the industry that I personally know use those.