You may have noticed that some things have changed in regard to localhost development on Mac OS X Leopard (10.5.5)

Namely, with the switch to Apache2, the configuration files are in new places...   this article will discuss what the new settings are and how to fix your configuration to support the new paradigm.  More than that, we’d like to share with you how to set up your localhost development so that your Parallels Windows instances will be able to see the sites you’re working on.

There are a lot of variations on this technique out there... some people use Bonjour, while others go into their windows configurations and edit subnet masks and the like.   I prefer this way of doing it because it touches the least amount of files, it’s simple, and it works.