Perfect.
I don't have an 840 to test with, but according to the device IDs it should be the file:
e1d6232.inf (for Win7 x86, or WinPE 3.x)
e1d6332.inf (for Win8 x86, or WinPE 4.x)
e1d6432.inf (for Win8.1 x86 or WinPE 5.x)
For x64 drivers you would use:
e1d62x64.inf (for Win7 x64, or WinPE 3.x)
e1d63x64.inf (for Win8 x64, or WinPE 4.x)
e1d64x64.inf (for Win8.1 x64, or WinPE 5.x)
Here's a download link for Intel's drivers, valid as of when I posted this:
http://www.intel.com/support/network/sb/cs-012904.htm
Download either the Windows 7 or Windows 8 package. In reality they are the same file and both Win7 and Win8 (and Win8.1) drivers are included.
Instead of running the exe package with the parameters to extract the drivers (which I always forget the command line to do) I would just use 7-zip and extract the files. Once they are extracted you can add the Win7/WinPE 3.x driver to the images. To do so, use the Add Drivers to WinPE tool and browse to PRO1000\Win32\NDIS62\e1d6232.inf. Add that driver to boot.wim and bootMedia.wim. Then browse to PRO1000\Winx64\NDIS62\e1d62x64.inf. Add that driver to boot_x64.wim.
Let me know if that driver works for you.
Thanks!