1. I want to add viewlet like the default news viewlet, but I can't write any ZPT. How can i do?

  You need not write any code. Just create a new Topic content to filter the content you need at any place you like. And add the Topic to your contentpanels and select the body viewlet. That is all. No code needed!

2. I just installed 1.5 and looked at the screenshot
http://www.plone.org/Members/panjunyong/ContentPanels/ContentPanels.JPG
and wonder how can you have different number of columns on different
rows?

 In fact, it is a combination of 2 contentpanels.  One contentpanels can be a panel of another one.  The bottom panels are in another contentpanels content.

3.  How can I disable the possibility of adding the Review List, Language, 
  Login, etc. from the Viewlets dropdown? Can we have some sort of 
  permission by which site admins can add any
  viewlet, while normal members can only add a subset of these viewlets?

  Yes, you can.  See ZMI portal_contentpanels. They are just actions. 
  You can define who can use the actions(use permission). 

4. It doesn't appear that the Zwiki viewlet is working anymore. I'm using the
latest CMFContentPanels 1.5.1a from sf cvs.  When I add a Zwiki page as a content panel, I am unable to view the content of the Zwiki page. Neither "Body" nor "Zwiki" appear in the dropdown of available viewlets.

  You must reinstalled ZWiki or installed ZWiki after CMFContentPanels.
You should reinstall CMFContentPanels.

