Lieberman was quoted in US News & World Report as saying categorically that he will not run as VP. It might seem more plausible if maybe he equivocated or was vague, but he said flatly that he'd done it before and had no interest in doing it again.
A lot of it, I think, depends on how much of a ruckus the social conservatives make over him through the rest of the primaries, he may be better off taking on Huckabee or someone else with more credibility in those parts. If he can't mobilize the gays/guns/god crowd, let alone excite them, he's in some serious mess. With the right mix though, he could play the fear card like Bush did in '04 and use the sitting president to his advantage (imagine the effect if the terror alert, for example, is raised periodically through the election and we have a sitting president threatening World War III or IV or whatever it is now).
I'd expect him to be a major force in the McCain campaign, maybe even a cabinet post or something if McMurder won though and absolutely a strong voice of the Likudist Israelis.