Hola
 
there is a problem that I sometimes encounter. When I am in paperspace, I will zoom to a particular detail to check how it will print, but sometimes double click in its box, which takes me into that particular details model space - I then find it impossible to get back into paperspace - Any ideas?
 

On the command promt type:
 
vpmax   and then hit enter
 
After that you click outside that box and then zoom out.
 
//Tobias

There should be a button for this, but sometimes this button is off.
In ACAD 2008 this button is located under the command area, next to the "snap,grid,ortho....." buttons. If  It´s not there click the small arrow in the lower right corner, on that menu check the line "Viewport maximize"
 
In ACAD 2009 the button is located closer to the arrow in the lower right corner.
 
Hopefully this helps you out!
 
//Tobias