A:  The documentation surrounding TRegIniFile is somewhat  sparse.  It is intended to work with 32 bit apps very much like  TIniFile worked with 16 bit apps.  The example below works as  follows:

button1:  Pressing this button will show how to get the keys  contained within a specified group (in this case, the debugging  section).  Included in this is an example of retrieving the  value of one of those keys (in this case, IntegratedDebugging  with a default value of 666).  The results are displayed in  ListBox1.

button2:  This one shows how to change an existing registry key  value to a new one.

Note the use of the try...except blocks.  This is always good  programming practice when dynamic memory allocaiton is used.
 

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  registry, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    ListBox1: TListBox;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
var
  reg: TRegIniFile;
  section: TStringList;
begin
  reg := TRegIniFile.create('software\borland\delphi\2.0');
  try
    section := TStringList.create;
    try
      reg.ReadSection('debugging', section);

      // This will read the entire section
      listbox1.items.assign(section);

      // This will read the assiciated value for one part of the section.
      listbox1.Items.add(reg.ReadString('debugging', 'IntegratedDebugging', '666'));

    finally
      section.free;
    end;
  finally
    reg.free;
  end;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  reg: TRegIniFile;
begin
  reg := TRegIniFile.create('software\borland\delphi\2.0');
  try
    reg.WriteString('debugging', 'IntegratedDebugging', '666');
  finally
    reg.free;
  end;
end;

end.