JQuery .submit function will not submit form in IE

I have a form that submits some values to JQuery code,which then which sends off an email with the values from the form.It works perfectly in Firefox, but does not work in IE6(surprise!) or IE7. Has anyone any suggestions why? greatly appreciated?I saw on some blogs that it may have something to do with the submit button in my form but nothing Ive tried seems to work.

Here is the form html:

<form id="myform1"> <input type="hidden" name="itempoints" id="itempoints" value="200"> </input> <input type="hidden" name="itemname" id="itemname" value="testaccount"> </input> <div class="username"> Nickname: <input name="nickname" type="text" id="nickname" /> </div> <div class="email"> Email: <input name="email" type="text" id="email" /> </div> <div class="submitit"> <input type="submit" value="Submit" class="submit" id="submit" /> </div> </form> 

and here is my JQuery:

var $j = jQuery; $j("form[id^='myForm']").submit(function(event) { var nickname = this.nickname.value; var itempoints = this.itempoints.value; var itemname = this.itemname.value; event.preventDefault(); var email = this.email.value; var resp = $j.ajax({ type:'post', url:'/common/mail/application.aspx', async: true, data: 'email=' +email + '&nickname=' + nickname + '&itempoints=' + itempoints + '&itemname=' + itemname, success: function(data, textStatus, XMLHttpRequest) { alert("Your mail has been sent!"); window.closepopup(); } }).responseText; return false; });