Here is the steps.
1. A 4GB pen drive (since the size of Windows 7 is 2.34GB)
2. Windows 7 installation files or a iso image of Windows 7 OS
3. Administrative privileges in the OS
Step 1 : Take the backup of all the data in your usb drive plug into the Machine.
Step 2: Go to device manager (Control panel –> device manager –> select disk –> select your usb drive ) and then right click –> properties –> go to policies –> Select Better performance). This step is needed for faster installation of windows 7 (You can wonder, windows 7 installed within 15 minutes with just 1GB RAM) See the following picture
Step 3: open the command prompt with administrative rights (Accessories –> right click Command prompt – and select run as administrator)
Step 4: type DISKPART (you will get a prompt as DISKPART)
Step 5: type LIST DISK (it will list all the disks), please remember the disk number of your pen drive (see the following picture)
So, mine is disk 1
Step 6: Execute the following commands one by one,
SELECT DISK 1
CREATE PARTITION PRIMARY
SELECT PARTITION 1
FORMAT FS=NTFS (since windows 7 permits only NTFS, the USBs also to be formatted as NTFS, and this process will take some time)
Step 7: Now insert the windows 7 DVD drive or if you have iso image, using winrar extract it to a folder
Step 8: go to the concerned folder in the command prompt (assume installation files of windows 7 as E:/win07)
execute the command in command prompt
BOOTSECT.EXE /NT60 G: (assigning the bootmanager to the USB. G is the drive letter for my USB)
Step 9: After getting the successful message, copy the contents of your Windows 7 installation files to your USB Drive. Thats it.
Enable Booting from USB option in your BIOS and lets see the installation will complete within 15 minutes.!!!!