An application is virtually certain to change design quite drastically from initial conception to launch. A well-conceived shell script that combines the application database schema with the Istarel Workshop Application Framework's object-relational mapping (ORM) tool makes it quite simple to cleanly handle change.
With the database and web server in place, I can turn my attention to PHP 5, my tool of choice for web development. MacPorts recently made this a much cleaner process. In the past, you needed to search for ports and variants (and hope that the key variants you needed were available). Now, installation is modular. As always, update MacPorts itself before proceeding with any installation.
Next up is the web server. Apache 2 comes pre-installed on Leopard systems (Mac OS X 10.5 and 10.6), but I want all my open source projects to work alongside one another.