Mac OS X Installer packages for Apache 2 and PHP 4.2.1 (Apache 2 DSO) are now available here. Just download, double-click, and you're ready to go.
Apache 2 is installed into /usr/local/apache2, so as to not interfere with the operating system supplied version of Apache.
[Editor's note: I haven't tried this Apache installer yet, so I can't vouch for what the package may or may not install and whether or not it works, but I thought some of you might be interested in trying it out.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020717015649681