program RegisterExt;

uses
  Registry;

procedure RegisterExtension(
  const sAppName: String;
  const sAppPath: String;
  const sIconName: String;
  const sExtension: String);
var
  Reg: TRegistry;
begin { RegisterExtension }
  Reg := TRegistry.Create;
  with Reg do
  begin
    RootKey := HKEY_CLASSES_ROOT;
    OpenKey('.ext', True);
    WriteString('', sAppName);
    CloseKey;
    OpenKey(sAppName, True);
    WriteString('', sAppName);
    OpenKey('DefaultIcon', True);
    WriteString('', sIconName);
    CloseKey;
    OpenKey(sAppName+'\shell\open\command', True);
    WriteString('', sAppPath);
    CloseKey;
    Free;
  end { with Reg };
end; { RegisterExtension }


begin
  RegisterExtension('MyGreatApplication',
                    'c:\program files\mystuff\myApp.exe',
                    'c:\program files\mystuff\myApp.ico',
                    '.shl');
end.