Is "Super Fetch" and "Ready Boost" services running on the computer? "Super Fetch" is the service that will fill all available RAM with things Microsoft thinks you might want to run at some point in time. Typically, inside of 5 minutes after a computer is turned on, the system will have less than 10KB (yes KB) free RAM, regardless of how much RAM the computer has.
Disable that stupid service, along with ReadyBoost. If those services are not disabled, you will never be able to get the computer to run the game smoothly.