1) Create NTFS partition in usb-key and make it active(primary) partition –
# cfdisk /dev/sdb

2) Create NTFS file-system the partition –
# mkfs.ntfs -f /dev/sdb1

3) Mount Windows iso and usb-key –
# mount -o loop win7.iso /mnt/iso
# mount /dev/sdb1 /mnt/usb

4) Copy over all files –
# cp -av /mnt/iso/* /mnt/usb/

5) Write Windows 7 MBR on usb-key –
# ms-sys -7 /dev/sdb

6) Keep a copy of the same as img –
# dd if=/dev/sdb of=/win7.img