Chad thats quite an extension of the FreeForm functionality. You will need to have a table to contain the comments. As well as a method for displaying and inserting them.
First question would be to see if the FreeForm license actually allows you to use it that way. Second question is how experienced are you at using PHP and MySQL?
If both those have positive answers then I would suggest taking a look at the extension hooks Solspace has made available to FreeForm and also take a look at the Development Documentation for EE.
Jamie
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