For exporting bitmaps of texture coordinates, I'd definitely look into the free version of UVMapper Classic (
http://uvmapper.com/). Using this, you'd save your AC3D object as an OBJ file and load it into uvmapper, then issue a "File | Save texture map" --- this allows you to export a texture map of the size you specify (without all that pesky resizing).
It's an extra step or two, but I think it's quicker and easier than trying to resize and cut along the edges to get the size of the texture map just right...