Boot able USb

1. USB flash drive with a minimum capacity of 4 GB.

2. Windows 7 Setup DVD.

Step 1 : Plug-in your USB flash drive.

Step 2 : Open the PowerShell (OR Command Prompt if PowerShell Not Exist). If you are using Windows 7/Vista then open it with administrator rights*.
* Goto Start -> All Programs -> Accessories ->Windows PowerShell -> Right-click on “Windows PowerShell” and select “Run as Administrator”.

Step 3: In the PowerShell, type
DISKPART
Now issue the following command:
LIST DISK

This will show you a list of available disks on your system. Disk 0 is usually the hard disk. note the size of your usb drive it may be disk 1 if no other disk is available but make sure to select your usb drive disk with its # (ex. diskpart> select disk 1)

Step-4: Now issue the following list of commands one by one as shown below:

CLEAN
CREATE PARTITION PRIMARY
SELECT PARTITION 1
ACTIVE
FORMAT FS=NTFS QUICK
ASSIGN
EXIT
Close Power Shell and proceed to the next step.

Step 5: Insert the Windows 7/Vista installation disc and note down the “drive letter” of your DVD drive.

open an elevated command prompt Goto Start -> All Programs -> Accessories -> Right-click on “Command Prompt” and select “Run as Administrator”.
Now type the following list of commands as shown below:
H:
CD BOOT
BOOTSECT.EXE /NT60 G:(NOTE:
G: is your USB drive letter)

EXIT

Step-6: Copy the contents of your Windows 7/Vista installation disk into the USB flash drive.
Directly Copy-Paste All DVD file into Usb Stick Then…

Your USB stick is now ready to boot and install the OS for you. Don’t forget to enable the “USB Boot” option and change the “Boot priority to USB device from hard disk” in your BIOS settings.

*Note you can also apply to win 2008 and other Os.