Create bootable flash drive for windows 7,vista using diskpart.

Put the USB Pendrive in the USB port on your computer.
Click "Start." 
Type "CMD 
cmd[rightclk]
run as administrator[clk]
YES[CLICK]

Type "DISKPART" in the command window that appears
Hit "ENTER" to execute the command
Type "LIST DISK" and hit "ENTER
." You will see a list of disks and their identifying numbers
 choose your USB pendrive drive number[for eg:1 ]
Type "Select Disk 1" 
hit "ENTER
Type "Clean
hit "ENTER
Type "Create Partition Primary"
hit "ENTER 
Type "Select Partition 1" 
hit "ENTER 

Type Active"
hit "ENTER
Type "Format FS=NTFS    ,this will take some time
hit "ENTER
Type "Assign
hit "ENTER
Type Exit"

Insert your Windows7  installation disk into your computer.
Go to "Start" and "My Computer." Note the drive letters for your computer's optical drive and your USBPendrive. Return to the command prompt window. For the purposes of this tutorial, it is assumed the DVD drive letter is G: and the USB PENDRIVE  is I:
Type "G: and hit "ENTER."
Type cd boot  and hit "ENTER

Type "bootsect /nt60 I:"    to create a boot sector on your USB key.

now copy all the contents of win7 dvd to the pendrive 
Thats it ,now we have a win7 usb bootable pendrive
RESTART YOUR PC
MAKE THIS USBPENDRIVE AS FIRST BOOTABLE DEVICE IN BIOS