Getting the Username from the HKEY_USERS values

Answer 1

If you look at either of the following keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\hivelist

You can find a list of the SIDs there with various values, including where their "home paths" which includes their usernames.

I'm not sure how dependable this is and I wouldn't recommend messing about with this unless you're really sure what you're doing.