Help with custom plugin for an action when new user is added

i want to listen for '

SIGNUP_USER_ADDED" ​

from amember available events..​

​

i wrote ​

custom plugin..shown in API/Hooks Manager.. like this..

class MyPlugin extends Am_Plugin
{
function onSIGNUP_USER_ADDED(Am_Event $event)​

{
$event->addReturn($event->getX() + 1);
}
}​

Two part question:
1. How do i get User object from Am_Event.. i am interested in getting username..
2. once i have Username.. how can i call other website on same domain like xxx.com?username=?????

I am still having issue with this.
I created the plugin below:

PHP:

<?php
class Am_Plugin_ivpmake extends Am_Plugin
{
    function onSignupUserAdded(Am_Event $event)
    {
        $user = $event->getUser();
        $r = Am_HttpRequest('http://dev.ivestplus.com/investage/userSignup.form');
        $r->send();
    }
}
?>

When I sign up, I am getting this error message:
Fatal error: Call to undefined function Am_HttpRequest() in /var/www/amember/application/default/plugins/misc/ivpmake.php on line 7

Any help would be greatly appreciated.

Made some headway. using "new" prior to "Am_HttpRequest" worked to hitting the outside server. However, I am not getting the user name.
Any ideas how to get user name to show at end of url?

Resolved: Thanks again for awesome support.
I am including what worked for me in case it helps anyone else.

PHP:

<?php
class Am_Plugin_ivpmake extends Am_Plugin
{
    function onSignupUserAdded(Am_Event $event)
    {
        $user = $event->getUser();
        $username = $user->login;
        $r = new Am_HttpRequest('http://www.myurl.com/platform/userSignup.form?username=' . $username);
        $r->send();
    }
}
?>