Ive got a powerBook g4 with 1.33 CPU, 2G of Ram, and ATI's 9600 with 64 mbs of ram - and this little monster doesnt like to render videos. Especially when - like working with motion - I draw a large vector, put it somewhere in 3d space, then fly around with camera with a lot of motion blur...
its said that its a common issue among G4s and its realted with insufficient VRAM.
however, there must be a solution! like editing firmware, so the graphics card uses some of the system ram (like the intel chipsets do).

If you want some samples, ill upload them.