Problem with WSAStartup, error LNK2001

I try to programme a simply FTP client.
I use 3 files: FTPconnect.cpp,FTPconnect.h,FTP.cpp.
I use Visual Studio 2008
compiles are all right;but when I built:
there are 2 error :
FTPconnect.obj : error LNK2001: unresolved external symbol
__imp__WSAStartup@8
fatal error LNK1120: 1 unresolved externals

what is the problem;
code as fellow:

FTPconnect.h:

#include<string>
using namespace std;
class FTPconnect
{
private:
    string state;
    int IPadr;
public:
    void open(string hostadr);
    void dir(string dirname);
    void get_in_dir(string dirname);
    void get_file(string filename,string localadr);
    void upload_file(string filename);
};

 FTPconnect.cpp:

#include "FTPconnect.h"
#include <iostream>
#include <Winsock2.h>
using namespace std;
void FTPconnect::open(string hostadr)
{
    if (hostadr == "")
    {
        cout<<"Please enter the FTP sites which you want login:";
        cin>>hostadr;
    }
    //$B=i;O2=(Bsocket

    WSADATA wsaData;
    int err;
    err = WSAStartup( 0x0101, &wsaData );
    if ( err != 0 ) cout<<"Error";
}

FTP.cpp:

#include "FTPconnect.h"
#include <iostream>
using namespace std;
void hint(string &command,string &information);
int main(void)
{
    string command,information;
    while(1)
    {
        hint(command,information);
        cout<<"command="<<command<<"information="<<information<<endl;
        if (command == "quit" || command == "bye")
        {
            cout<<"GoodBye"<<endl;
            break;
        }
        command = "";
        information = "";
    }
    return 0;
}
void hint(string &command,string &information)
{
    string input;
    int local;
    cout<<"FTP>";
    getline(cin,input);
    local = input.find(" ");
    if (local == string::npos)
        command = input;
    else
    {
        command = input.substr(0,local);
        information = input.substr(local+1);
        cout<<"Has space"<<endl;
    }
}