Копирование методом потока.

procedure FileCopy(Const SourceFileName, TargetFileName: String);
var
S,T : TFileStream;
begin
S := TFileStream.Create(sourcefilename, fmOpenRead );
try
T := TFileStream.Create(targetfilename, fmOpenWrite or fmCreate);
try
T.CopyFrom(S, S.Size ) ;
FileSetDate(T.Handle, FileGetDate(S.Handle));
finally
T.Free;
end;
finally
S.Free;
end;
end;