After learning this awesome trick you can install Windows 7 from pen drive. The advantages of this trick are as follows:

1) You can install Windows within 15 minutes
20 You can also install Windows on those systems which dont have CD or DVD drive.

Tools Required:
1)Pen Drive with a minimum space of 4 GB
2)Windows 7 setup DVD.

Now, just follow the steps below:
STEP-1 Plug in your pen drive copy all your data stored in the pen drive and format the pen drive.
STEP-2 Go to start -> all programs -> right click on command prompt -> click on run as administrator.
STEP-3 Type diskpart and hit enter this will start the microsoft diskpart utility.
STEP-3 Now type List disk and then type select disk 5. Note:- If your pen drive is installed in disk five then type disk five otherwise select your pendrive's disk.
STEP-4 Now enter the following commands one by one:
clean
create partition primary
select partition 1
active
format fs=ntfs quick
assign
exit