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As both Josh and Joe said, unfortunately you can't convert them... I'd use this opportunity to consolodate forms (if possible), and use all of the cool new features in forms 2.0 within the new forms!
Also, some of the coding is different from forms 1.0 to forms 2.0, so just make sure that any custom coding you might have is compatible with the new forms. (Sorry, off-hand I'm not sure what the differences are, but I know there were some threads about it)