Changing Map Projection Dynamically

[Bill Thoen]

This has probably been asked before, but I can't find any info on it. 
Basically, I'd like to know how to change the map projection in 
MapServer as I zoom in to a larger scale map view. Specifically, I start 
at a national scale using a Lambert projection, but when I zoom into a 
state scale, I'd like to choose a more appropriate projection (like 
State Plane).

Can this be done easily with a map file or an HTML template? What's the 
best way to solve this problem?

- Bill Thoen