Автор: http://www.swissdelphicenter.ch

uses
  ShellAPI;

function InstallINF(const PathName: string; hParent: HWND): Boolean;
var
  instance: HINST;
begin
  instance := ShellExecute(hParent,
    PChar('open'),
    PChar('rundll32.exe'),
    PChar('setupapi,InstallHinfSection DefaultInstall 132 ' + PathName),
    nil,
    SW_HIDE);

  Result := instance > 32;
end; { InstallINF }

// Example:

procedure TForm1.Button1Click(Sender: TObject);
begin
  InstallINF('C:\DelphiWorld.inf', 0);
end;