Pandora

Pandora simplifies the process of stitching together a sequence of panorama images.

Load all the panorama pieces (in order) as layers inside an image (suggestion: make a new image then "Open as Layers" and select all the files). Then run Filters->Combine->Make Panorama.

You still have to do the detailed matching by hand, but Pandora calculates the needed image size, moves all the layers to approximately the right position and creates appropriate layer masks for fading each image into the next.

http://shallowsky.com/software/pandora/