Open Source software in a Windows environment?

From AskSlashdot: “Like many people, I work in a Windows NT/2000 shop that has absolutely resisted bringing *nixes into our environment. Everyone has their reasons – my boss has resisted because it would be more difficult and expensive to find a replacement admin if I leave, since said replacement would need to be able to administer both Windows and *nix boxes, which I can understand. But I’m still curious…”