Computer skills are transferable. There is a fallacy that learning an alternate-computing platform is somehow a hindrance to learning Windows. This assumes that computer skills, once learned, are intransitive. The truth is that once a computer user learns to use a mouse or trackpad they can use such a device on any computer that utilises one for input. The same is true for a keyboard, monitor, scanner, CD-ROM drive or any other peripheral device.
Transferability goes well beyond hardware.
It exists for software as well. Both platforms utilise very similar principles and concepts that apply to both. The real differences are in the finer details, like managing and viewing files and navigating the computer. In terms of software, Windows and Macintosh applications are so similar in the basic ways of doing things that no user would have much trouble using either platform. If a person learns to use one of those programs on Windows or on Macintosh, they will quickly be able to use the other platform's version.