Living with Windows: Security
Network World, By Rich Mogull
Under ordinary circumstances, and in the hands of an educated user, a properly configured Mac is not much of a security risk. Sharing a network with Windows systems doesn't change that; the Mac is still relatively safe.
Under some circumstances, however, even a properly configured Mac, with an educated user, can compromise the security of the Windows systems to which it's connected. But that risk is easy to manage with a few simple precautions.