There is a [**Code Preview Handler**][1], but it supports only the extensions .cs, .vb, .js and .sql . The source code is available and it doesn't look too complex to create a Preview Handler (well, sort of, I wouldn't know how to do one).   

I tried adding other extensions to the Code Preview Handler with the tool [**Preview Handler Editor**][2] but it doesn't work, the preview pane is blank (at least for the .pl files I tried).

![alt text][3]

**Edit**: you have also a pack of Preview Handlers [**here**][4], that support the following filetypes:

    * ActionScript (.as) 
    * ASPX (.aspx)
    * C# (.cs)
    * CSS (.css)
    * Diff (.diff, .patch)
    * DOS (.bat, .cmd)
    * JavaScript (.js)
    * Ruby (.rb, .rhtml, .rjs) thanks to Ivan Porto Carrero
    * SQL (.sql)
    * VB (.vb)


  [1]: http://timheuer.com/blog/archive/2006/12/13/13945.aspx
  [2]: http://blogs.msdn.com/toub/archive/2006/12/14/preview-handler-association-editor.aspx
  [3]: http://img260.imageshack.us/img260/1686/capturelj.png
  [4]: http://blog.tatham.oddie.com.au/2006/12/20/vista-and-office-2007-preview-handler-pack-released/