You may want to try the Zoom property for the slide view. This example is from the PPT 2003 VBA Help file. Not sure if the property is available in earlier versions.

[vba]
'Sets the zoom of the current view to 400%
'Value is 10-400
Windows(1).View.Zoom = 400
[/vba]

An issue is that I cannot determine a method to position a specific part of the slide in the viewable area of the window. If you can somehow capture the x,y coordinates of the area the user clicked, looks like you could use the ScrollIntoView method to correctly position that area.

Cheers,
James