preg_replace and ereg_replace

[Anon]

I have a segment of code that is inside <code> and </code> tags.

How do I replace that text in between the tags with it's highlighted version?

I know i'd use highlight_string, and currently what I've gotten is this:
preg_replace("/<code>/(\w+)<\/code>", highlight_string($1), $message);

or this:

ereg_replace("<code>(.*)<\/code>", highlight_string($1), $message);

Which is not helpful at all.