GeoTiff Layer & World Files

Hi, users!

We are using the Image Tile Layer in OpenMap and are having some difficulty registering our images.  We have been getting our imagery from Terraserver, but their world files are in UTM coordinates.  With the provided world file, the images do not show up.  Using some known coordinates (pulled from Google Earth), I can iteratively tweak the world file and get a pretty close fit, but this is a very time consuming and somewhat haphazard process. 

Terraserver does provide top-left and bottom-right lat/lon coordinates for the image.  Without a suite of GIS tools, does anyone know how to build a world file that we can actually use?

Thanks in advance!

Chris