Man, if it were just as easy as having someone "telling" you how to do it, I imagine that there woudl be a lot more bboys and bgirls out there.

But my suggestion (as I myself cannot do them yet either) is to get a good video or a friend who can do them well, and just watch it and break it down.
First step is figure out a good entrance, whether from the ground or on your feet. I mean, you'll six-step into it sometimes, but it seems to be easier to get the momentum going if you're on your feet. The first swing's pretty easy, just plant your lead foot and then swing the other one into the direction you intend to spin, and follow the movement through, but the hardest part is learning where and when to plant your hands, to push your body off the ground. From there, it's a matter of maintaining the momentum.
Check out
http://www.style2ouf.com, they have a lot of videos on there, check out the battle vids for the most instances of windmills.
I'm probably no help whatsoever, so I'm gonna stop now.