How to display a formatted message in plain text?

Here's the scenario:
- preview is turned off
- a message header is selected (in Inbox)
- display the message (in plain text) within a new popup window

Basically, I turned preview off because I was getting zillions of web bugs,
and some of the junk mail is so well-crafted that I can't tell if it's
legitimate. So, currently I save suspect emails to a text file and look at
them with a text editor, but that is a ridiculous pain-in-the-butt.

Thanks!
-dan