With a three button mouse, you zoom in with Button 2, and out with Button 3. 
With a two button mouse, you zoom in with Button 2 and out with Shift-Button 2.
On Windows, you can control this with the padinit file.

The "hand" mode in the drawing tools is for navigating. 
With the left button, you can pan and follow links.
We call this the "Run" mode.

When in "Run" mode (with the hand cursor), the arrow keys
will pan, and the page up/page down keys will zoom.

Clicking on the color swatch in the drawing tools will bring 
up the color tools.

Holding down the Control key in any mode will let you pan 
with the left button.

Holding down the Alt key in any mode will let you zoom.  
Zooming works like it does with the magnifier tool.  
Click zooms in.  Click-drag sweeps out a region to zoom into.  
Shift-click zooms out.  Shift-click-drag sweeps out a region 
to zoom out from.
