Using DW CS5.5 with PHP file extensions and no testing server with no server side code in the pages. As the title shows when I go to preview in any browser only the code is displayed.
Yep, that is normal behaviour and has nothing to do with Dreamweaver.
A browser interprets HTML, CSS and JS, but not PHP. For a browser to interpret PHP you will need a server to compile the file into an HTML document on the fly.