<script src="@Url.Content("~/Scripts/jquery-1.4.4.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery-ui.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery.unobtrusive-ajax.js")" type="text/javascript"></script>

<script src="@Url.Content("~/Scripts/jquery-1.5.1.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery-ui-1.8.11.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>
    <script src="@Url.Content("~/Scripts/jquery.unobtrusive-ajax.min.js")" type="text/javascript"></script>

<configuration>
  ...
  <appSettings>
    ...
    <add key="ClientValidationEnabled" value="true" />
    <add key="UnobtrusiveJavaScriptEnabled" value="true" />
    ...
  </appSettings>

$(function () {
    $jQval.unobtrusive.parse(document);
});

function partialViewLoaded(request, status, partialViewId) {
    if (request.responseText != "") {
        //Hook validations on elements of the loaded view
        $.validator.unobtrusive.parse($(partialViewId));
    }
}

@using(Ajax.BeginForm(new AjaxOptions{
                           UpdateTargetId = "loginForm",
                           OnComplete = "partialViewLoaded(xhr, status, '#loginForm')" })){

$.ajax({
     url: "yourURL",
     complete: function(xhr, status){
         partialViewLoaded(xhr, status, "#loginForm");
     }
});