Editing the XML directly
First let me take a moment to tip my hat to Splunk for the new dashboard editor in Splunk 4.3. There are only of a couple of reasons why you would still need to edit simplified XML dashboards: forms and post-processing data. I predict that these reasons will go away in the future as more features are added to the dashboard editor.
Note
The documentation for simplified XML panels can be found by searching splunk.com for Panel reference for simple XML.