That's just not true. In the May 15, 2007 Republican debate, he stated he favors "an assault weapons ban." Last month on meet the press, he said he "would have supported the original (1994) assault weapons ban." There is no EXISTING assault weapons ban, so he favors a change in law.
In 1994, he said he would support the AWB. In the debate you cite, he said again that he would have supported it.
He does not support a new AWB. There’s a press release posted to FR, December 31, 2007, that details exactly what he supports, and it includes a detailed description of what he considers weapons of unusual lethality.