the n900 can't have multitouch due to hardware limitation .
however , fake multitouch is possible , you touch the screen at one point and then touch it at another point , the position of the second point can be calculated , given the first point remains staitionary .
example : for pinch zoom , you keep one finger stationary and move the other finger away from it , but if you move both fingers , nothing will be detected , the screen reports the average position of all points it's touched at , so moving 2 fingers away , the screen will return the same point (no motion detected)

anyways , this fake multitouch isn't used in any applications on the n900 , except maybe a demo of the idea on youtube.