PNAC official website
an anti-PNAC website
even-handed wikpedia entry on PNAC
long video on PNAC's effect on Bush's war plan
Generally, the PNAC is a bunch of neoconservatives (including Cheney, Rumsfeld, Wolfowitz, etc.) that want a form of global imperialism to be a paramount goal of American foreign policy. This involves doubling the military budget and engaging in unilateral military action in foreign countries without provocation if it means that American ideals can be spread and we can gain access to the quckly depleting natural energy materials. Now, this is obviously not a complete explanation (and admittedly a biased one) but read the links and you will have a more complete idea of what the PNAC is all about.
To me, it looks like it is hard to deny that Bush is following more of a PNAC agenda than a Republican one and, as a result, I'm concerned about the country's future. America is not meant to be an imperialist war state. I believe that the agressive nature of the PNAC agenda will only serve to embolden the terrorists. I'm not saying that we shouldn't do what needs to be done to stop them, but we should be careful to only do what needs to be done - the fear of terrorism should not be a free pass for Bush to invade at will. If Bush is really using 9/11 as an excuse to implement the spread of neocon PNAC policy, I think the terrorism problem will only get worse.
There is a whole other argument to be made against implementation of a PNAC-themed foreign policy - based on the negative effect it will have (is having) on the American economy - but I think this post is already long enough.