José Prado came up with a MooTools-powered extension called Lighter.js that provides syntax highlighting capability. Using it can be as simple as adding a single script to your webpage, selecting the elements you wish to highlight, and Lighter.js takes care of the rest. Just call the mootools and lighter JS’s in your site header and wrap the code around <pre id="Code" class="code">some code</pre>

More info: Lighter.js