Thanks Rush and Coldfire for that.
I have another way.
then you have created succesfully USB bootable.
Requirement----4GB or more space USB and Windows 7 ISO or DVD
1.Plug your USB in port.
2.Open CMD in admin mode.
4.then LIST DISK
5.now if your USB is showed in DISK 1 then write --- SELECT DISK 1
CREATE PARTITION PRIMARY
SELECT PARTITION 1
write them one by one.
7.type ASSIGN and hit enter and EXIT.
now enter windows 7 DVD into your rom and then know the drive letter.
8.if your dvd drive is H, then first type H:
then another disk process starts and then you type CD BOOT
then type BOOTSECT.EXE /NT60 G: [think your USB drive is G]
It doesn't work in XP.in XP you will have to use Windows PE for that.