I'm not going into the comparison part coz I don't have the time for it rt now!
U know telling them what linux is, isn't important. At home, I never told them what Linux is or what to do with it. They just saw me things on a "different looking windows". They often complained, that this virus has got into windows, blue screen got while playing a game. But they never saw anything like that when I used to do my task on "different looking windows". Sometimes windows used to blow up because of its infections, over fiddling with system files/registry hacks that mah bro used to do or some "unknown causes" that left me scratching my head! Often the case was that I didn't have the time to rectify the problems, so I told them to work on that "diff. looking windows".
Once, For a week I had exams and nobody complained that they cudn't do this and that, as listening to music, watching movies, browsing the net and making/printing document is all they did. I already told them to browse the applications menu and use wateva they liked. Though my bro. complained about games, but he didn't shout much. He often appreciated and liked mplayer/xine over WMP as they played movie dvd ISOs directly and took a lot a less time to open and play any video/movie. That was fedora core and now my bro loves customising things with beryl on UBuntu on another computer. Installing is as easy as windows as he needed to know the meaning of only the root partition which he asked. Its simple!!
So if u r putting too much burden on ur mind becoz of that, then experiment and see for urself!! Take it casually, like u don't care. If u'll try to teach them tooo much, then obviously they'll get scared like u r tryin to teach them something difficult!! Its in human nature. So let them explore.
People often think that u'll have to teach them dis an dat. Just make em treat it like "different windows" and let them play with it themselves!