Zooming by defining rectangle and changing viewbox atttributes

hi
i am naveen. i am implementing zoom in zoom out effect in my application using svg document.I my application i have box in which i see zoom in zoom out tools like when i click it. 
my problems:
1.It should change the mouse cursor to zoom type.
2.When i click on svg document it zoom in or zoom out depending on tool which i select.
3.When there is a zoom i have to check wheather it goes out of the browser view we have to get the scroll bar to see the zoom effect.