Polar Stereographic projection Extent

[Ryan Ollerenshaw]

I am having a bit of trouble figuring out the extent I should use to 
display the entire northern hemisphere using the Polar Stereographic 
projection.  The best that i have been able to come up with is:

EXTENT 3000 2000 4000000 3000000

but this only displays the right half of the norther hemisphere, how can 
i display the full 360 degrees of the northern hemisphere all at one 
time?  When using a polar projection i am not sure what the extent 
numbers actually represent.  They cant be corner points because the 
display should be a circle, so what are they offsets from?  Any clarity 
that someone can provide on how to use polar projection would be very 
helpful. Thanks.

PROJECTION 
     "proj=stere"
        "lat_ts=75"
        "north"
        "lat_0=90"
  END