This is how you create a bootable usb to install Windows 7 (NON EFI):

Attention, make sure you understand every step before executing it. If not used correctly can result in fatal dataloss.

Assumptions:

USB stick with ~4GB: /dev/sdb (change device according to your setup, don’t overwrite your second harddisk!)

Get the iso

Visit http://mirror.corenoc.de/digitalrivercontent.net/ and download one via torrent

Wipe the device

If you’re like me and tried to dd the iso to your usb stick or created multiple partition tables in this process, better wipe your stick.

wipefs -a /dev/sdb
dd if=/dev/zero of=/dev/sdb bs=512 count=1 conv=notrunc

Partition and format

Delete everything, create one partition with ~4GB, MBR table, bootable flag.

fdisk /dev/sdb

Format using ntfs:

mkfs.nfts /dev/sdb1

# Create a label for use in the bootloader
nftslabel /dev/sdb1 winboot

Copy the data

mount -o loop ~/windows.iso /mnt/iso
mount /dev/sdb1 /mnt/stick
cp -rv /mnt/iso/* /mnt/stick/

Install grub as bootloader

Note: Keep /dev/sdb1 still mounted

grub-install --target=i386-pc --boot-directory="/mnt/stick/boot" /dev/sdb

Configure grub

Edit /mnt/stick/boot/grub/grub.cfg:

default=1
timeout=15

menuentry "Installation" {
    insmod ntfs
    insmod search_label
    search --no-floppy --set=root --label winboot --hint hd0,msdos1
    ntldr /bootmgr
}

menuentry "First hard drive" {
    insmod ntfs
    insmod chain
    insmod part_msdos
    insmod part_gpt
    set root=(hd1)
    chainloader +1
    boot
}

Unmount and Installation

umount /dev/sdb1

And now, try to boot the stick. Have fun!

Create Windows 7 bootable installation usb