I'd like to be able to set the absolute width of the current extent, given a particular height/width of the map control and a center point. Here's something along the lines of what I'd like to do:
Public Sub SetMapDisplay(ByVal CenterPoint As LatLong, ByVal Width As Double)
Any way I can create a RectangleShape for the extent based on screen height/width and a given map width in the unit of the base map?
You can set the current extent of the map based on a center point and a width but the width has to be in world coordinates. We have a sample in the Code Community that does something like that. The project Center Map based on Lat.Long will show you how to do that. Note that in the sample there is also a projection dimension for going from Lat/Long to the Google projection (Spherical Mercator).
code.thinkgeo.com/projects/show/centermapbasedonlat
A similar project Center Map on Moving Vehicle will also help you for your task.
code.thinkgeo.com/projects/show/centeringonmoving