There are several articles discussing how to set it up on the Mac and I found this one from Florian Kubis to be the easiest to follow.
If you are using homebrew as your package management system instead of MacPorts, you should use this tutorial instead.
The tutorials also cover npm (the package manager for node.js) and express (a Web app framework built for node.js)
There is no MacPorts ports for npm and express yet, maybe someone should create them?
Several slides and quick intro about node.js:
- "Evented I/O based web servers, explained using bunnies", the idea behind node.js in 10 pages
- "Node.js and websockets intro", a bit more technical than the bunnies example
- "Running YUI3 on node.js", integration with YUI3, moving client js to server side without any changes!