minimizing window...Question?

ok i have a question about my mac minimizing windows i have an aluminum macbook 2.0 with the latest updates and everything but when i minimize a window the window does not curl up or bend like this

http://www.mactips.org/wp-content/Slow-Motion-Minimize.png

instead my mac just will go like a windows manchine it will just get smaller and minimize and get smaller but it wont bend like this ones or my cousins white macbook any ideas