Assuming that your searching when your certain the user is logged on, i.e. during login, you can check:

code:
 
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\DefaultUserName

This lists the last user logged in which is also your current user in this case, also assuming you have not disabled the "List Last Logged On User" at CTRL-ALT-DEL policy.

-Jim
_________________________
-Jim

...the sort of general malaise that only the genius possess and the insane lament.