procedure TForm1.Button1Click(Sender: TObject); 
var 
  reg: TRegistry; 
begin 
  reg := TRegistry.Create; 
  reg.RootKey := HKEY_LOCAL_MACHINE; 
  reg.OpenKey('Software\Microsoft\Windows\CurrentVersion\SETUP', False); 
  ShowMessage(reg.ReadString('SourcePath')); 
  reg.CloseKey; 
  reg.free; 
end;