Success!

It took me only 3 evenings in elapsed time, but the dryer belt is replaced thanks to Appliance Parts on Blossom Hill, judicious study of Internet how-to articles (which appear to be more or less just copies of each other), and good old observation.

Our dryer flat out stopped spinning the drum. After a few Google searches it was likely that the dryer belt was bad, and that was confirmed when I found the old belt under the dryer. I didn't realize at first, but dryers are really just boxes of sheet metal held together with little plastic clips and a few screws. When you know where to pull a dryer quickly comes apart. The mechanics are super simple, too: A motor, a pulley, a belt around the drum. Once you figure out in what sequence to install the parts, and where to thread the belt (belt around drum, put pulley in place, loop belt through pulley, then around motor axle), with help holding the drum in place, this was really just a 15 minute job start to finish.

I guess most of the $100 I saved by doing this myself pay for the knowledge of doing this efficiently.