From my experience, IIS has alwasy been the easiest (especially IIS 5.0). I am not trying to take anything away from UNIX/LINUX, but for applications and usability, I would go with Windows 2000 and IIS. I have setup numerous Windows 2000 servers running IIS and they are yet to crash or be hacked into. But, the Windows OS kernel does not prevent DoS or DDoS attacks. If you are extremely worried about this, then go with Linux, RedHat or Slackware. If you have a good firewall, then I would go with Windows 2000. Just my 2 cents.