ZOOM Centering Help

I’ve been working creating an interactive display map for a client. I’ve figured out the controls I’d like to use for moving the map, but I’m having trouble with the zooming features.

What I’d like to do is have the user click on the “+” button to zoom in and the “-” button to zoom out. The problem is the map is not centered when the user clicks either button?

Any ideas how I can fix this, or improve it?

Any help is greatly appreciated. Sorry its not the full flash file, it was 400K.