Many times we need to know if a TCP port is open or not, here I leave a function to perform this task using winsock.

Code tested in Delphi 7, 2007 and 2010.

uses
  Winsock;

function PortTCP_IsOpen(dwPort : Word; ipAddressStr:AnsiString) : boolean;
var
  client : sockaddr_in;
  sock   : Integer;

  ret    : Integer;
  wsdata : WSAData;
begin
 Result:=False;
 ret := WSAStartup($0002, wsdata); //initiates use of the Winsock DLL
  if ret<>0 then exit;
  try
    client.sin_family      := AF_INET;  //Set the protocol to use , in this case (IPv4)
    client.sin_port        := htons(dwPort); //convert to TCP/IP network byte order (big-endian)
    client.sin_addr.s_addr := inet_addr(PAnsiChar(ipAddressStr));  //convert to IN_ADDR  structure
    sock  :=socket(AF_INET, SOCK_STREAM, 0);    //creates a socket
    Result:=connect(sock,client,SizeOf(client))=0;  //establishes a connection to a specified socket
  finally
  WSACleanup;
  end;
end;

see this sample of usage

begin
 if PortTCP_IsOpen(3306,'127.0.0.1') then 
  DoMyStuff();
end;