Skuzzy, you are right, unix/linux is easier to secure...maybe because it was meant to be a part of the network.
but this does not make windows unsecure. as i said, if you armove a flawed stuff and secure windows box well, it's pretty good.
Stability is another case. Unix-like systems are by fare more effective (as i'd call it).Then i'd say AD (based on ldap) and AD-like mamagement makes windows (in my eyes) by far better back-office system. everything about windows AD is just great
You could try ISA server as a firewall... but after playing with it for about a year i say, it's nowere close to what unix/linux can give you.