using wininet to upload file for a password protected server

Hi,
I'm trying to use the wininet for uploading file to a server which requires
authentication. i checked a bit in the web and found that i have to first use
an empty request to perform the authentication and only afterward on the same
request send the data.
problem is - if i do that, the second request is sent empty (but it passes
the authentication), if i don't, the request is sent without the
authentication data (and failed).
any idea why?

here is the code:
hSession = InternetOpen("Test",
                              INTERNET_OPEN_TYPE_PRECONFIG,
                              NULL,
                              NULL,
                              0);


    hConnection = InternetConnect(  hSession,
                                    server,  // Server
                                    INTERNET_INVALID_PORT_NUMBER,
                                    NULL,    // Username
                                    NULL,    // Password
                                    INTERNET_SERVICE_HTTP,
                                    0,        // Synchronous
                                    NULL);    // No Context


    INTERNET_BUFFERS BufferIn = {0};
    DWORD dwBytesRead;
    DWORD dwBytesWritten;
    BYTE pBuffer[1024]; // Read from file in 1K chunks
    BOOL bRead, bRet;

    BufferIn.dwStructSize = sizeof( INTERNET_BUFFERS );

    HINTERNET hRequest = HttpOpenRequest(hConnection, "POST", targetURL, NULL,
NULL, NULL, INTERNET_FLAG_RELOAD | INTERNET_FLAG_NO_CACHE_WRITE |
INTERNET_FLAG_KEEP_CONNECTION, 0);
    if (!hRequest)
        return OnExit(GetLastError());

    // cchUserLength is the length of strUsername and
    // cchPasswordLength is the length of strPassword.
    char strUsername[64], strPassword[64];
    strcpy (strUsername,"username");
    strcpy (strPassword,"password");

    DWORD cchUserLength = sizeof(strUsername);
    DWORD cchPasswordLength = sizeof(strUsername);
    InternetSetOption(hRequest, INTERNET_OPTION_USERNAME, strUsername,
cchUserLength+1);
    InternetSetOption(hRequest, INTERNET_OPTION_PASSWORD, strPassword,
cchPasswordLength+1);

    // at this point normal authentication logic can be used. If
    // credentials are supplied in InternetConnect, then Wininet will
    // resubmit credentials itself.  See HttpDump Internet Client SDK sample
    // for more information.
    if (!HttpSendRequest (hRequest, NULL, 0, NULL, 0))
        return OnExit(GetLastError());

    
    // Read all returned data with InternetReadFile ()
    do
    {
        InternetReadFile (hRequest, pBuffer, sizeof(pBuffer), &dwBytesRead);
    }
    while ( dwBytesRead != 0);


    HANDLE hFile = CreateFile (uploadFile, GENERIC_READ, FILE_SHARE_READ, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hFile == INVALID_HANDLE_VALUE)
        return OnExit(GetLastError());

    BufferIn.dwBufferTotal = GetFileSize (hFile, NULL);

    if(!HttpSendRequestEx( hRequest, &BufferIn, NULL, HSR_INITIATE, 0))
        return OnExit(GetLastError());


    DWORD sum = 0;
    do
    {
        if  (!(bRead = ReadFile (hFile, pBuffer, sizeof(pBuffer), &dwBytesRead,
NULL)))
            break;

        if (!(bRet=InternetWriteFile( hRequest, pBuffer, dwBytesRead,
&dwBytesWritten)))
            break;

        sum += dwBytesWritten;
        progress = sum;
    }
    while (dwBytesRead == sizeof(pBuffer)) ;

    CloseHandle (hFile);

    if(!HttpEndRequest(hRequest, NULL, 0, 0))
        return OnExit(GetLastError());

    return OnExit(0);