uses IdMultipartFormData;

{ …. }

procedure TForm1.Button1Click(Sender: TObject);
var
data: TIdMultiPartFormDataStream;
begin
data := TIdMultiPartFormDataStream.Create;
try
{ add the used parameters for the script }
data.AddFormField(′param1′, ′value1′);
data.AddFormField(′param2′, ′value2′);
data.AddFormField(′param3′, ′value3′);

{ Call the Post method of TIdHTTP and read the result into TMemo }
Memo1.Lines.Text := IdHTTP1.Post(′http://localhost/script.php′, data);
finally
data.Free;
end;
end;