Sure, you can have dependencies go up. Check out the sample doc here:
http://blog.omnigroup.com/2006/09/21...d-sample-file/
In that plan, the arrow from task 9 to task 8 goes up. To draw a dependency arrow, hold down shift and draw a line from the start or finish of one task to the start or finish of any other task The toolbar is just a shortcut for the most common case, since people tend to put the first tasks at the top of the list and have their arrows go down.