Avoiding Microsoft Lock-ins?

bayduv1n asks: "My company relies on WinNT primarily for workstations, file servers, and print servers. In my opinion, Linux based solutions are close to offering a viable alternative. I'm sure that management, however, would like to see mainstream acceptance in the corporate world before considering a migration from the current environment. With the Linux drum beating louder and louder, I would like to make recommendations that would leave our future options *open* and avoid locking into MS technology. I consider a lock-in anything that makes it difficult to migrate. One example of a current lock-in is the macros written for Excel. These would require significant effort to migrate to Staroffice Calc. Implementing MS Metadirectory Service could also be classified as a lock-in. My question is: 'What recommendations can I make now to make it easier to migrate to Linux in a couple of years?'"