I am very interested in buying Unity Pro,and a Mac for it 
I was looking at the iMac… do you think the Radeon X1600 card is powerfull enough to make a 3d game with shaders and complex scenery?
Thanks
Yes. Especially if you intend on selling the games you make any time soon, you will most likely want/need to support cards much slower than that.
-Jon
I have a 7300 (which is generally an inferior card to the X1600) and Unity runs beautifully on my machine (even with World of Warcraft running in the background ).