Based on my experience of having done this a few times(!), the most important registry keys are:
HKEY_CURRENT_USER\Software\Borland\Delphi\5.0\Known Packages
HKEY_CURRENT_USER\Software\Borland\Delphi\5.0\Library
and possibly
HKEY_CURRENT_USER\Software\Borland\Delphi\5.0\Known IDE Packages
and maybe
HKEY_CURRENT_USER\Software\Borland\Delphi\5.0\Palette
HKEY_CURRENT_USER\Software\Borland\Delphi\5.0\Palette Defaults
So long as you have done a standard D5 installation first.
It's easier/more reliable to let the IDE fill in the other bits as you start using it and you change options as appropriate. Some component packages, eg madExcept, DevExpress etc are often best re-installed using their own installers anyway.
Unless you're going to have multiple users on the same machine using Delphi then the HKLM stuff isn't really all that important - I don't think.
As a related aside - I have learned that a good way to handle this is to build a FinalBuilder script (or similar) to set up my Delphi environment each time I decide to use a new machine/installation. I copy/download/checkout (which can be done in FB too) all package source then use FB to compile it, copy it, create dirs, and fill in the appropriate registry keys etc. I always get a consistent environment and makes it much easier to rebuild individual components or packages as and when they get upgraded too. The items can also be put into the script in 'dependency order' so that you know to re-compile a dependent package if something else changes. I now have a single FB sciprt that builds D5, D2007, D2009, D2010 environments and packages of all my main components, all depending on which compiler(s) I'm interested in which I indicate by a simple variable. Well worth it.