こんな感じで

void __fastcall TADataModule::NMUDP1DataReceived(TComponent *Sender, int NumberBytes, AnsiString FromIP, int Port)
{
　　scoped_array<char> buf(new char[NumberBytes+1]);
　　int s = 0;
　　TNMUDP& aNMUDP = dynamic_cast<TNMUDP&>(*Sender);
　　aNMUDP.ReadBuffer(buf.get(), NumberBytes+1, s);
　　buf[s] = 0;
　　// ...
}