Alternatives by Russell Brown can be found in his tutorials for Photoshop CS4 Extended at The Russell Brown Show: Spherical Panorama (at AdobeTV) and Advanced Spherical Panorama Stitching Techniques.
Last and not least, see Carl Larsen's a nice 4-part tutorial on Building a Cube World in After Effects, and his Horizon replacement with Mocha for AE v2 at Toolfarm.
Oh, and of course the camera-aware Trapcode Horizon was built for this purpose (video tutorial).
Update: a few more resources that popped up covering the various wrinkles in general subject...
- Mark Christiansen explains some in After Effects Script of the Week: pt Panorama.
- The options have improved in Photoshop by CS5.5; see info in Help (1, 2) and various resources from Richard Harrington.
- Also, AE Scripts released Edge blending, a solution by erLab to build up panoramic projections with 2 or more projectors. This script will create the necessary comps for you render and be able to create this using standard video projectors.