The other thing you have to remember (which Tiger Shark touched upon) is that the information given to the President (whoever happens to be holding the post at the time - and this applies to other world leaders as well) was in a highly condensed form, probably edited to fit on one page. He would not have got the full information, because it's just not possible. Could you imagine what would happen if a leader of a country received every piece of paperwork produced by one department (e.g. the Foreign Office, or whatever the US equivalent is)? They wouldn't be able to take it all in - hence why they have advisors, deputies, heads of departments etc. to do this for them. The last person who is likely to know what is going on in the White House/Congress/the Senate is the President - he has a million other things to worry about.
Now I don't normally defend George Bush (or America to be honest) but I think in this situation he is being blamed (as are his top advisors) for something they may have known next to nothing about. American media is too quick to point the finger at someone, and this is being used by the Democrats to push whoever they're putting up for election (John Kerry last time I checked). When a group of terrorists bombed a Spanish train station in the early hours of the morning, you didn't see everyone turning round to the government there saying "you should have known about this - it's all your fault, why didn't you do something about it?" - and if they did it certainly wasn't blown out of proportion (ok so there was a backlash in the general election a couple of days later, but that's to be expected following such an event - people have their views altered temporarily in the face of tragedy).
I can see September 11th becoming like Bloody Sunday is over here - a tragedy that happened several years ago but no-one wants to drop the subject until someone carries the can for the event. So far Bloody Sunday has cost over £250 million - mostly in legal fees - do you really want that amount of your taxes wasted trying to blame someone for September 11th?
