Smooth scrolling webpage

I want to make a webpage were you can click a button and the webpage will scroll to the next div.

Not just vertically but also horizontal & diagonal.

Here are some examples of what I'm trying to achieve:

http://www.melissahie.com/
http://www.teamviget.com/
http://www.nofrks.com/

Does anybody know how to do this? Or can someone point me in the diection of a good tut?

tia