WinPE is the boot environment that is used by many tools (WDS, AIK, imagex) to deploy images.

Initial step is to create a source PC (install OS and apps), sysprep and capture.
*this was done for an XP machine, you have more flexibility with Windows 7, but each XP machine type has a unique HAL which can’t be captured easily.

Basic instructions were found here:

There are a few ways to automate a PE.

Seeing as the base instructions use a boot.wim, you will need to make any changes to that image using imagex:
imagex  /mountRW  boot.wim  1  d:\mount
-make changes to d:\mount\windows\system32\startnet.cmd
-also add imagex.exe somewhere in d:\mount 
imagex /unmount d:\mount /COMMIT

Copy the udpated boot.wim to your USB stick (\sources) created above.

-use CALL in you batch file if calling another .cmd file
-use wpeutil reboot to reboot as needed

imagex command-line reference
imagex Apply an image
Creating a bootable WinPE 2.0 USB Key