I have it (Mucho Macho edition) for my iBook G3900, 384 ram/ 32 vram. It runs ok.. but as your city grows it starts to bog down.
These types of games are very deceiving, the graphics may be nothing spectacular but there is a lot for the processor to keep up to pace with. Every citizen is doing a task, thinking, something, every building, industry, farm, hotel, etc are all keeping track of cost, maintinence and profits. and as the city grows there is a lot to keep track of so i would assume it slows down as it gets really cpu intensive with all those factors and more to keep track of.
the city i am on is approx 400 people and and you can account for every one on screen, you see them runing around going to work, church, hospital, caberet ;oP etc. I have even tried lowering the graphics setting but it doesn't make much difference. as I'm sure its not the graphics that slow it down.