edit a page without unpublishing

hi,
how can I edit a published page on my site without having to unpublishit. I mean if I edit a published page I may choose to preview my changes before it being visible to the site users.
thanks..

What you are looking for is workflow, which is to be included in an upcoming release. The simplest way to handle this for now is to duplicate the document you want to edit, make changes to the duplicate, preview it then copy the new version to the old page OR change the links on the site to the duplicated page.