This may well turn into a media firestorm. Some of these things were already known, but there are some others that should at the very least prove disastrous to his candidacy if they turn out to be true, and the media actually publishes it. It's hard to predict exactly how this will go, as the book doesn't come out for another two weeks, and the quote from the Kerry adviser indicates they're gearing up to return fire in a big way. Even if the worst accusations don't prove to be true, if the Kerry camp isn't able to quash this adequately, it could still be devastating for his campaign.
On the flip side, if it does turn out that a Bush supporter is behind this (which may be true, monetarily — I wouldn't imagine it would be cheap to ram such a controversial and conservative book through writing, editing, and publishing in a few months) the possible trouble for Bush is relatively low, even if it turns out to be all distortions and lies. There's little chance Bush approved it personally, and he can always point out other, similar movements on the left (speaking of distortions and lies, Fahrenheit 9/11 springs to mind).
Should be interesting to see how this plays out.