I asked about this once before, but just recently discovered a program (free) that does it. (Sorry, I can't add it to my previous post, because I couldn't find the original post.)
It's called "Win32 Disk Imager" (Ver 1.0).
I imaged my working 4gig sd card from the card reader ('device'). The program saved it to C:\Users\user\downloads\ by choosing 'Read', and left 'Read Only allocated partitions' unchecked. I then removed my card from my card reader, added an empty 4 gig card, and chose 'write'. It took about 20 minutes to do it's thing.
That's about it. I don't know if the 'Read Only allocated partitions' box has to be left unchecked or not. I've used it for a day now, and all seems to be well.