Microsoft Knowledge Base Article 310426 contains the following summary:
This step-by-step article describes how to use features in
Registry Editor that are included in Windows XP and Windows Server 2003, but
that are not included in previous versions of Windows. In Windows XP and later,
Regedit.exe is the only Registry Editor tool that is included in the operating
system. Regedt32.exe is no longer a part of Windows XP or Windows
Server 2003. A primary use of Regedt32.exe that was missing from earlier
versions of Regedit.exe , was to set permissions and other security settings
for registry keys and subkeys. That feature is now available in the version of
Regedit.exe that is included in Windows XP and Windows Server 2003.
Note: If you try to start the Regedt32.exe tool in the Run dialog box of Windows XP or Windows Server 2003, Regedit.exe starts, and Windows does not generate an error message.
The version of Regedit.exe that is included in Windows XP and Windows Server 2003 includes the Permissions and Favorites features. The Favorites feature was first introduced in the Microsoft Windows 2000 version of Regedit.
You can use the Favorites feature to put frequently-used registry subkeys on a list that is accessible on the Favorites menu. To do so, click a subkey, and then click Add to Favorites on the Favorites menu, type a name for the Favorites listing or accept the default name. The default name is the name of the subkey. The listing is then available on the Favorites menu, and you can click the listing to return to the subkey. To delete a listing, click it on the Favorites menu, click Remove Favorite, and then click OK to confirm the deletion.
The security features that are available in Regedit.exe include assigning permissions, auditing access to the registry, and assigning ownership of a registry key.