I found this tutorial and these two especially helpful, as well as the Drupal page (which, since it was the first place I went, was probably the victim of all my newbie errors). What made it all work for me, after several WSODs:
0. Starting with a fresh MAMP (and why not, dmg is so easy),
1. Before doing anything else, I gave php.ini a memory_limit of 128M.
2. I made sure there were no other copies of apache or mysql running -- including any that started from previous failed installations!
3. I didn't bother to change the default name and password for mysql (bad! bad!)
4. In the MAMP app, I changed the default ports to standard for apache and mysql (80 and 3306, not 8888 and 8889, respectively).
5. I didn't try to outsmart the installer; I just BOMAArchiveHelper.app'ed a fresh drupal download into htdocs and browsed to http://localhost:80/drupal-7.x-dev/ -- note port 80, localhost, and not localhost.local. Then when the installer told me to copy default.settings.php to settings.php, I did what it said. Otherwise, settings php was untouched.
6. The install then proceeded normally.