If you want to get up and running quickly using Drupal on Mac OS 10.5 your best bet is to use MAMP, as John VanDyk suggests in his comments. There are MAMP setup instructions on Drupal.org.

But I decided to try moving away from MAMP. One reason is that MAMP doesn’t come with certain features — for example, I’m told that it’s hard to get SSL working. Another is that the upgrade cycle for PHP and MySQL is different from that of MAMP, and I sometimes want to be able to roll my own upgrade on my own timeframe.