Sorry for late reply, just saw this today.
Since ArcReader is non authoritative, don't think this is an option by design.
The only way I know of to do what you ask in Reader, is to right-click on the layer and "zoom to layer extent".
then, use the identify tool to open the identify window, and change the "Identify from" dropdown to the layer in question (Hydrants in this case). Then, using the identify tool, drag a box around the entire display. This will populate the identify window with all the hydrants within your selected area. Will give you a total count at the bottom left, and you can scroll through the results with the mouse, scrollbar or arrow keys.
Hope this helps, though I'm sure not what you were hoping for.
R_