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I _think_ that you get penalized for having duplicate content when you have duplicate content. IOW, if you intend to put the same basic content in just a more print friendly format, I think you will be penalized.
I also _think_ the preferred method for doing this is by providing a CSS stylesheet change which would _not_ be a different page per se.
Ask in the CSS forum if you need to know how to do this.
Most of the time search engines do a decent job of listing the "real" page instead of the printer-friendly page.
But like Elijah said, just be safe and block the robots to them.