Geographically square pixels

[pw]

Hello,

In my configuration file (.map file)  if  I have an image
that is projected with equal area degrees pixels,
(ie: each pixel is evenly sized in 'seconds' not feet or meters)
how can I set up mapserver to know what scale
the pixels are in the X and Y direction for the raster?

I have been looking at the proj4 manual and at the
mapserver manual and there doesn't apper to be any
way to define the extents of an input raster in degrees
so that it can be mapped to, say, lambert.

Thanks for any insight,

Peter