USDA Hardiness zones in digitized form?

[Erich Schroeder]

Hello;
  I've been asked to produce a series of maps of plant
distributions for an in-preparation publication.  The
authors want to have the recent USDA hardiness zones as
a backdrop.  Does any one know if these have been digitized?
I'll want to be able to import them into a GIS (ARC/INFO), so
there will have to be some information on the projection, or 
better yet, it should be in latitude/longitude.

Thanks
Erich Schroeder
Illinois State Museum GIS lab
schroede at denr1.igis.uiuc.edu