In an IT environment, appropriately configured, I will say this with 100% certainty, Windows XP is as secure as OS X...period. End of story. Personally I wouldn't use OS X on a Mac. I would probably go with a stripped down version of BSD....yah I know OS X is based on BSD but OS X's, especially Leopard's, security is interesting. Especially its built in firewall. Its just a theory but a lot of OS X's API and front end makes me wonder how much of that is open to the possibility of hacking the OS. No the Army should grab BSD and build their own UI for it. OS X is a fine OS...for consumers. In a mission, and security critical roll I simply don't trust it...It really hasn't had a trial by fire yet in a larger scale corp environment. When half the corp world is going OS X, then lets talk.