I always suggest to not try 2 changes at once. It just complicates things if there is a problem.
My suggestion is to leave the current 4GB in the system and then install Windows 7 64bit. Make sure everything is working well and there are no problems with the install, drivers
, configuration, etc.
Then add the new RAM.
If it were me I would remove the 2x2GB sticks and install the new 2x4GB sticks in the same slots and test (that computer boots and runs Windows, then with Memtest86+).
If all is good then I would add the 2x2GB sticks into the remaining slots and test again.
This just makes diagnosing any problem that might arise easier. No need to work backward.