Map tiles and max/min latitude and longitude

Question

I'm trying to build a map based on a center point lat/long, the map will always be a fixed size say 1024 by 1024. The user can chance the center point and zoom.

If I populate the map with map tiles from map quest for example, is there someway I can know the max/min latitudes of the map currently being displayed?

I want to know this so I can accurately project things onto the map.

Thanks