Now, I need to backup again to an image file, but the image have the sdcard space size (15Gb) and not your distro size (about 3Gb).
I'm using Win32DiskImager.
If You need only personal backup, and You don't plan to write this image on a smaller sdcard, I think one of the best option just create image and then compress it with rar,tar,zip etc.
To create the image for a smaller card - maybe more time consuming.
First I change the size of the root system using gparted in linux. In windows You can do it with Acronis Partition expert or a similar program (with Acronis Partition expert You also can extend partition on whole size of sdcard after writing some small image on it). After resizing Root Partition I copy only half
of the card with dd:
sudo dd if=/dev/sdd of=linaro-raring-server-xbmc-0.1-4gbcard.img bs=1024 count=3400000
It looks that there is no chance to copy part of disk with Win32Imager. But You can try "dd for windows" http://www.chrysocome.net/dd
(Be careful to use right command and drive, otherwise You will crush Your data !!) After creating smaller image it also can be effective compressed.
By the way, how can I install in the NAND?
I didn't tried yet to build nand image. I plan to use this article: http://linux-sunxi.org/LiveSuit_images