How can I setup a regular expression to replace nested text with replacement text. I can't explain it very well, but say I want to replace [asdf] with <asdf>, and my sample text is:

Code:
[asdf]adsfasdf[asdf]adsfadsf[/adsf][/adsf]
I end up with this:

Code:
<asdf>adsfasdf[asdf]adsfadsf</adsf>[/adsf]
Or something similiar depending on the modifiers I use.

How can I accomplish replaces like this?