1. How can I format SD card as EXT2 ...Can you explain ?

First, you need a linux. For simplicity, you can download an Ubuntu live CD (www.ubuntu.com), then you'll be able to boot from CD and format the SD card from there. There's a nice partition editor by default in ubuntu.

Under linux, run commands by following steps below:

1. Plug in your SD card into your computer
2. Open Terminal, run command "df", you should see your media card device name like "/dev/sdb1" which mounted as "/media/disk"
3. Unmount the SD card by running command:
sudo umount /media/disk
4. Format your SD card by running command:
sudo mkfs.ext2 /dev/sdb1
5. Remount your SD card by running following two commands:
sudo mkdir /media/disk
sudo mount -t ext2 /dev/sdb1 /media/disk
6. Go to the directory where the rootfs.tar.gz was saved, and extract all the files in rootfs.tar.gz into your SD card by running command:
sudo tar zxvf rootfs.tar.gz -C /media/disk
7. Your SD card is ready.