Moving Small Organizations from Windows to Linux?

chris1646 asks: "Currently we are a small organization that is entirely a Windows shop. Next year much of the server and desktop hardware we run will need replacing. I am looking for creative ways to introduce Linux as my desktop and server OS of choice, however a couple of our core applications run exclusively on Windows. Has anyone had any success hosting Windows applications via terminal server while using Linux as the client OS? Has anyone handled a AD to open source LDAP migration?"