Okay, so that would what, theoretically fix the buffer overflows that were supposedly already fixed by the non-execute blocks?
What about that big target, the C$ share used on every Windows box by default, that Windows needs to run properly, that you can't change the security options of, that 'hides' itself ever so poorly, and that every hacker knows about?
What about a firewall that when detecting a program using a socket communication will allow it to communicate while it pops up a window asking you if you want to block it?
What about the million and one services turned on by default, that almost no one uses a ton of, that are just waiting for a hacker to connect to?
Need I go on?
M$ knows security like McDonald's knows filet mignon.
Maybe Windows Vista really will be different, but I doubt it. They might fix a few things, but I doubt they'll really make it all that secure.