[Proj] how to use proj to project images?

[Britton Kerin]

I have a radar swath that I would like to map project.  From the oribital 
geometry, I can get a geographic lat/long for any pixel in the image, and 
then proj can take me the rest of the way.  But I don't think I want to do 
that for every pixel in the image.  Is it reasonable to project a grid of 
points and then linearly interpolate for pixels between grid points? 

Also, I'm not exactly sure how to assign the values of individual pixels 
in the projected image.  Rotating a pixel looks like it would  require 
averaging its value of the new pixels it covers after rotation.  If anyone 
has any pointers to a description of he most accepted way to do this I 
would appreciate it.

Thanks,
Britton