I've searched and have not found a good answer to this question. I'm planning on buy a new iMac, I'm planning on upgrading it to the 256mb card. I'm doing this because I will also install windows on it to play games. I don't care that the 24" imac video card is possibly replaceable. What is the performace differences between the ATI and NVIDIA video cards? Does one have a noticeable advantage, and because the NVIDIA is powering a 24" monitor with higher resolution will that have an effect on performance? Hope you guys can help, thanks.