New
#31
It appears that Optimus is part of the Nvidia graphics driver available on the Dell Support Downloads webpage. Optimus Technology
I see no other software for enabling it after reinstall, although the Dell-provided Intel chipset might be needed after trying the ones Win7 wants from installer and Windows Updates. Be sure to enable Automatically get recommended drivers and updates for your hardware (Step 3) before running all rounds of Important and Optional Updates with reboots.
Make sure the Dell Downloads model page Dude linked matches your tag number for specificity and if not reinput your tag number on the Driver downloads page. Product Support for Alienware M14x R2 | Dell US