This is a neat tip from Allen Bauer in a newsgroup posting recently. The question was related to how you can revert back to old settings after installing a rogue component/app that damaged some of Delphi's registry settings (library path).
One thing you can do with all versions of Delphi from at least D5, is use the "-r" command-line switch. This allows you to specify the root registry key to use when loading the IDE. For instance in D7, you could export the HKCU\Software\Borland\Delphi key to a file. Then rename the "Delphi" key to something else, like "SafeMode". Then re-import the exported key to recreate the HKCU\..\Delphi key. Finally, when you run the Delphi32 application, just pass the "-rSafeMode" switch to use that key.
This, by the way, is how JED's Delphi Configuration Manager works.