People who are new to the concept of wikis often ask for a way to approve edits before they go live.

Most wikis do not support such a feature because this goes against the very spirit of being open and quickly editable. Implementing an approval workflow can greatly hinder wiki adoption and nullify the positive effects a wiki can have.

Have a look at this post for some more discussion about this topic.

Also checkout http://www.wikipatterns.com for more tips on how to make a wiki successful.