I suggest you use HttpRequest to emulate the login progress,use HttpResponse to get webserver response and content and use global CookieContainer to store the cookies.
When you get login successful message,you can use other HttpRequest with global CookieContainer to get any web pages you want download or access.
you can use Httpwatch(www.httpwatch.com) to watch how Internet Explorer exchange data with WebServer.you can also use IE9 devloper tools to do this(press F12 in IE9).
In this case.
1.You should GET http://forum.soundarea.org/index.php?app=core&module=global§ion=login page's source code.You will see
ipb.vars['secure_hash'] = '880ea6a14ea49e853634fbdc5015a024';
880ea6a14ea49e853634fbdc5015a024 is secure_hash.
2.Post to http://forum.soundarea.org/index.php?app=core&module=global§ion=login&do=process Page. Use this parameter:
auth_key=880ea6a14ea49e853634fbdc5015a024&ips_username=test&ips_password=pass&rememberMe=1
and get the cookie.
3 . Get any page you want with this cookie.