How can I restore the registry keys from another C drive on Windows 7 64-bit?

It goes without saying that you should back up all your user data first and anything important on the broken machine. As you should be aware, there are risks in doing this, and really the easiest thing would be a full install - and to not mess with the registry. But, that of course is up to you. However, you may see latent issues if/when you get Windows back up...

Here is a pretty good guide, I used it once when I was in IT (though that was a while ago).

You should be able to load the other drive's Hive file and restore that way:

EHOW Run-Through

1. Login to your other Windows drive
2. Type "regedit.exe" into the search box
3. Expand "HKEY_LOCAL_MACHINE", click "FILE" > "Load Hive", navigate to your broken drive.
4. Browse to "Windows\System32\Config", select a Hive file from the list (SAM/Security = User Rights / Passwords, System = OS, Software = third party)
5. Click "Open" and name it, click OK
6. Modify away, though this will be pretty manual.
7. Left click Hive, "File" > "Unload Hive"