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.

Good for you!

"inch by inch, slowly I turned......I mean it's a cinch.

Yeah, I second that - Good for you!

Congratulations.

Which desktop environment did you choose?

Edit: I did'nt realize its an old thread. I may not get the answer.

I used XFCE (on Debian Squeeze). It is sufficiently bug-free, user friendly, and has a small footprint (Gnome has a significantly bigger footprint). I did run into a bug that most likely had to do with the translation files.
I did install some extra software like VLC and Gimp, because we were already using that in Windows. That doesn't come with the desktop (luckily IMHO). I recently discovered the archive manager coming with XFCE is crud. It is much better to install file-roller. So maybe you'd want to tweak the default installation of XFCE a little (afterwards via aptitude).
Hope that helps.

Can you make xfce to look windows-like? A desktop which can do that would be best for migrating users to linux.

Try: http://zorin-os.com/

and http://rikkiendsley.com/?p=115

Pretty much most Linux OSs can look* like any sʍopuıʍ or on, freedom; bliss.

LXDE may be the best. Other ones often mentioned are icewm, enlightenment and fluxbox.

For me it was an issue of making it look like Windows XP. Admittedly that might have helped my case: XFCE looks more like Windows XP (on resource friendly "bare" mode), than Windows 7 (on minimum graphics mode). I'm sure IceWM has a Windows XP theme; I didn't bother for the eventual system. In fact ATM I have an unusual theme.
My approach was stressing the difference, and providing Windows as an option. If you don't have Windows, it might be a good idea to get a Windows-like theme. If you want a pretty alpha blended effect-filled desktop, Gnome could be a better choice. Also, if you have the resources, you can look into running the Windows installation through a VM. Then Linux would become The system that does everything. I've seen this setup. It is another good approach to get the technical impaired to use Linux.
BTW Debian is very versatile and lets you choose the DM very dynamically.(I.e. after installation, and not limited to one.)