Problems with creating a bootable drive with Win7 on a Mac

Hello. Im having troubles turning my external harddrive into a bootable drive with win7 ultimate 64 bit for my new computer. Furthermore, I'm supposed to handle this on a Mac. I will list up what i did, and hopefully you can tell me what i did wrong:

- Partitioned my external harddrive to MS-DOS (FAT)
- Used terminal to convert the ISO to a IMG by using: hdiutil convert -format UDRW -o /Users/Rasmus_Hansen/Desktop/windows7.img /Users/Rasmus_Hansen/Desktop/windows7.iso
- Used terminal to transfer the IMG to my external drive by using: sudo dd if=/Users/Rasmus_Hansen/Desktop/windows7.img of=/dev/rdisk1 bs=1m

Everything seemed to play out as i wanted. However, when i tab f12 and select my external drive as the boot device, I still get the message:"Please select a proper boot device....."


What have i done wrong?



In advance, thanks.





NB: answers in english as well as in danish works for me.