<form action="http://YOURWEBSITE/index.php?option=com_acymailing&ctrl=sub" onsubmit="if(!this.terms.checked){alert('Please accept our terms and conditions');return false;}" method="post">
 <table class="acymailing_form">
 <tr>
 <td><label for="user_name">Name</label></td>
 <td><input id="user_name"   type="text" name="user[name]" value="" /></td>
 </tr>
 <tr>
 <td><label for="user_email">E-mail</label></td>
 <td><input id="user_email"   type="text" name="user[email]" value="" /></td>
 </tr>
 <tr>
 <td><label for="user_html">Receive</label></td>
 <td><input type="radio" name="user[html]" value="0" id="user_html_0" ><label for="user_html_0">Text</label><input type="radio" name="user[html]" value="1" id="user_html_1" checked="checked"><label for="user_html_1">HTML</label></td>
 </tr>
 <tr>
 <tr>
 <td colspan="2" ><input type="checkbox" value="1" name="terms" /><a href="linktoyourterms">Terms and conditions</a></td></tr>
 <tr>
 <td colspan="2" ><input class="button" type="submit" value="Subscribe" name="Submit" /></td>
 </tr>
 </table>
 
 <input type="hidden" name="acyformname" value="formAcymailing1" />
 <input type="hidden" name="ctrl" value="sub"/>
 <input type="hidden" name="task" value="optin"/>
 <input type="hidden" name="redirect" value="http://YOUR_REDIRECT_URL"/>
 <input type="hidden" name="option" value="com_acymailing"/>
 <input type="hidden" name="visiblelists" value=""/>
 <input type="hidden" name="hiddenlists" value="YOUR_LISTS"/>
 </form>