DISM: Offline driver injection
To Add a Device Driver to an Offline Windows PE Image
In this step by step guide we are going to inject Windows 7 Intel LAN drivers to our existing boot image, I have an existing C:\winpe_x86 directory with the boot image (BOOT.WIM) and the LAN drivers (LAN folders) already copied.

1, Go to Start > All Programs > Microsoft Windows AIK > Deployment Tools Command Prompt > right-click and select Run as administrator

2, Mount the base image by using the DISM tool to a local Windows PE directory by typing the following command:
Dism /Mount-WIM /WimFile:c:\winpe_x86\Boot.wim /index:1 /MountDir:c:\winpe_x86\mount
3. Next is to add the .inf file(s) to the base image with the dism command with the
/Add-Driver option
Example: Dism /image:<path_to_image> /Add-Driver /Driver:c:\winpe_x86\mount\Windows\driver.inf
as for the actual driver:
Dism /image:c:\winpe_x86\mount /Add-Driver /Driver:C:\winpe_x86\LAN\Intel1\E1K6232.INF
repeat this step for additional driver.

4, After injecting the needed drivers we must unmount the image using the following dism command:
Dism /unmount-wim /Mountdir:c:\winpe_x86\mount /commit
Now we need to make a bootable media (CD-ROM or UFD) to test our boot image.