Here at home I'm sort of the admin (although in admin terms I'm a terrible noob). We really needed a new PC at home so I was the one appointed to that task.
For some time I had been fiddling with Linux, in such a noobish way that I had become very confident in installing Windows after Linux. :-[ Also I was comfortable with setting up Debian.
So first I got the PC and installed Debian. I didn't expose my family to the PC until I had installed all the software they'd be nagging about and there were no problems with it. I took the time to choose a desktop environment and acquaint myself with it. Also, I had to wait for the Windows CD to arrive. It might be relevant to note that for video's, office and browsing (the normal usage) there wouldn't be much difference for everybody, because we used free cross-platform programs anyway.
When I installed Windows, I didn't install Flash in Windows, and I made Grub choose Windows by default. That was a "trick" I used. At first they were reluctant. But I said Flash under Windows is just too big of a security risk. So if they wanted to visit sites with Flash, they had to restart in Linux. Enter the long-winding explanation of Grub. I had to explain that most, if not all functionality of Windows was present in Linux.
Second "trick" I used, was starting the PC my self under Linux. I could myself leave an instance of Opera open, and my family would unsuspectingly find themselves working in Linux. I had set-up automount and some shortcuts to folders of theirs in Linux, so they would be able to find their files (unless they saved to the Windows desktop :
) I had chosen two completely different desktop backgrounds for Linux and Windows so the difference was obvious to them.
Eventually Linux wasn't scary anymore; in fact it was preferable. They got tired of switching to Linux in Grub. So I was so kind to change the default.
Now my whole family spends most time on the computer in Linux. I have also installed Linux on a laptop for them (they asked it). I don't expect to lose Windows for quite some time, for hardware support reasons, but I got my family here understanding why that sucks.