I use Photostitch (freeware) which came with my Canon, and it gets decent results.
Download here: (Cannon site, File is called k7a21enx.exe)
Some examples of it's results by a pro photographer here:
http://www.kenrockwell.com/canon/photostitch.htmEDIT: Just noticed the system requirements only mention XP SP2, but it works fine with SP3.