How to determine map extent question?

[Paul Maine(ATS)]

I am writing a mapserver application that will geocode a street  
address. I desire to plot a point in the center of the map( that is  
the street address ) and then draw a concentric circle about the point  
with a radius of 3 miles. How can I determine the extents of the map  
so that I can request the appropriate size map? I desire the map  
itself to be able to show local street names in a city.

Thank you in advance for such an active news list with excellent  
advice and assistance.

Paul Maine