There are 640C
drivers in Windows 7, at least in my x86 install, do you show those for your x64 install? You might have to do the Windows update button to see them and they are not listed with other Deskjet
drivers, but farther down the list.
You might also want to research how to restore the Print Spooler in case of problems. I used the Deskjet 820C x64
drivers on my x64 install and they locked up my system and resulted in keeping the Print Spooler from starting. They worked fine on my x86 install. I am told you are only offered drivers relevant to your install, but because of my experience, I am not so sure the x64 drivers were not really x86.