With my Wordpress.org installation, I couldn't get the Accepted Answer here to work (not sure if that's only expected to work with Wordpress.com?)...
I ended up using the SyntaxHighlighter plugin instead.
With that plugin, at first, your code will appear escaped in 'Preview Changes' view: It will appear correctly then after publishing. I think thereafter publishing it will then appear correctly in 'Preview Changes' (not 100% about that).
