When start RegEdit, you will see the following subtrees under the "My Computer" header:

HKEY_CLASSES_ROOT
Contains software settings about drag-and-drop operations, handles shortcut information, and other user interface information. There will be a subkey for every file association you have defined.

HKEY_CURRENT_USER
Information regarding the currently logged-on user (see HKEY_USERS below).

• AppEvents: contains the settings for which sounds to play for system sound events
• Control Panel: Control Panel settings are stored here, similar to system.ini and win.ini in Win 3.x.
• InstallLocationsMRU: appears to contain paths for Startup folder programs
• keyboard layout: specifies current keyboard layout
• Network: Network connection information
• RemoteAccess: Contains information about the current log-on location if using Dial-Up Networking
• Software: Software configuration settings for the currently logged-on user.
  
  

HKEY_LOCAL_MACHINE
Contains information about the hardware and software settings that are generic to all users of this computer. Subkeys include:

• Config: Configuration information
• Enum: Hardware device information, such as monitor settings
• Hardware: Serial communication port information and settings.
• Network: information about networks the user is currently logged onto.
• Security: network security settings.
• Software: Software-specific information and settings
• System: System startup and device driver information, and operating system settings.
  
  

HKEY_USERS
Information about desktop and user settings for each user that logs onto this computer. Each user will have a subkey under this heading. if there is only one user, the subkey will be ".default"

HKEY_CURRENT_CONFIG
Contains info about the current hardware configuration, pointing to HKEY_LOCAL_MACHINE.

HKEY_DYN_DATA
This key contains dynamic information about plug-n-play devices. The data here changes if devices are added or removed on-the-fly (i.e., hot-docking).