Animation playback problem

In the 2.49(a), blender the animation system is running REALY slow, like 10 fps!.. its horrible. In simple files its no so bad, but like in the Mancandy files its horrible, and in the 2.48(a) the animation goes well, with no delay.

Does anyone had/have this problem also?
thanks for the help in advance!

ps: i have a ATI Radeon HD 2400 PRO.