You can create a livecd Using UNetbootin, download it from the USC, and run it, once it loads you can select the distro you would like to make a livecd of,or of you already have the iso you can choose it, then select your SD card and off you go.
Also you can Install UNR on the SD card , of course if there is enough space for it, and if you have another USB device.
To Install the OS on the SD card this is what i did (you need 2 USB devices or 2 SD card with 4GB+ available):
- Create a livecd using UNetbootin
- Connect both devices to your PC
- Make sure you select the livecd to boot into it
- Once you're on the livecd mount the other USB/SD device
- Format it to ext4 or w/e Filesystem you want to use
- Make Sure that you choose the USB/SD card when asked where to install Ubuntu (i unplugged my HDD's to avoid any confusion, but just by looking at the GB count you'll know )
- Now you must wait for it to finish, since it is an SD card it will take like 2 hours or more. (when i installed it, i chose not to install updates or 3rd party , 'cause it's going to take more time)