I'm sorry to say we actually removed the markup editor as of Confluence 4.0, you can read more about this and the reasons why here: http://blogs.atlassian.com/2011/11/why-we-removed-wiki-markup-editor-in-confluence-4/
Unfortunately it isn't possible to edit in markup now, although you can still use the Source Editor plugin to edit the source of the pages but it is now in XHTML format rather than wiki markup so it won't give the same effect as working with the old wiki markup.
All the best,
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