<script language="JavaScript">
    function showLDiv()
    {
    if(  document.getElementById("loginDiv").style.display == 'none' )
         document.getElementById("loginDiv").style.display = ''
    else document.getElementById("loginDiv").style.display = 'none'

    return false;
    }
    function check_form()
    {
    if(document.forms["form_login"].req_username.value=='' || document.forms["form_login"].req_username.value=='') {
    alert('Оба поля обязательны для заполнения');
    return false;
    }
    return true
    }
    url=document.URL
    if(url.indexOf("login.php")==-1  && document.getElementById('navlogin')){
    document.getElementById('navlogin').innerHTML  = "<a href=\"login.php\" onclick=\"return showLDiv()\"><span>Войти</span></a>"
    login = "<center><div id=loginDiv style=\"display: none; \">"

    login += "<form id=form_login name=login method=post action=\"login.php?action=in\" onsubmit=\"return check_form()\">"
    login += "<fieldset>"
    login += "<legend>Введите ваше имя и пароль ниже</legend>"
    login += "<input type=hidden name=form_sent value=1 />"
    login = login + "<input type=hidden name=redirect_url value="+document.URL+" />"
    login += "<br><table width=\"100%\" align=left>"
    login += "<tr><td align=left><b>Имя :</b></td><td align=left><input type=\"text\" id=\"fld1\" name=\"req_username\" size=\"30\" maxlength=\"25\" /></td></tr>"
    login += "<tr><td align=left><b>Пароль :</b></td><td align=left><input type=\"password\" id=\"fld2\" name=\"req_password\" size=\"30\" maxlength=\"16\" /></td></tr>"
    login += "</table>"
    login += "</fieldset>"
    login += "<p class=formsubmit><input type=submit class=button name=login value=\"Войти\" /><br /> <a href=\"register.php\">Еще не зарегистрированы?</a><br /> <a href=\"login.php?action=forget\">Забыли пароль?</a></p>"
    login += "</form>"
    login += "</div></center>"

    document.getElementById('pun-navlinks').innerHTML += login
    }
    </script>

    <style>
    #loginDiv{
        position:absolute;
        z-index: 2;
        background-color : Green;
        border : solid;
        padding-bottom : 5px;
        padding-left : 5px;
        padding-right : 5px;
        padding-top : 5px;
        width: 300px;
    }
    </style>