Thanks for the tip, Jim! Unfortunately, Autostitch could not detect a panorama in my images. My overlaps must be too small. But I did find a solution that had been right under my nose. Photoshop CS4 has improved upon its 'photomerge' feature from previous versions. There is a new mode called 'collage' which can rotate and scale composite pieces and it was able to combine my photos without a hitch.

Here is the output...

View it larger HERE.

Thanks for looking!