an ac to dc converter is just a rectifier which can be 4 diodes arranged in a diamond shape for a full wave rectifier. You can also buy a rectifier which does it for you with 4 legs. While I do not think using a windmill on your car is an especially easy or inexpensive way to charge your ipod...
I have had cars from 1963 to 2006 and they have all had cigarette lighter sockets.
It is fairly easy to add, they are sold in auto parts stores.
You should connect the cigarette lighter (12v socket) to the fusebox or if you connect directly to the battery use an inline fuse of 5 or 10 amps...