Joe Lieberman hurt Al Gore more than Dick Cheney helped Dubya. Lieberman was a poor choice in an attempt to distance himself (Gore) from Bubba. Al Gore should have picked Bob Graham and he would have won Florida outright. Maybe Jeanne Shaheen to help in New Hampshire or Jay Rockefeller in West Virginia.
NH and WV are two very small states and while Gore would win either of those he easily could lose another state and thus lose altogether. I dont really think Shaheen would have helped Gore win any Bush states other than NH and Rockefeller other than WV .