As you may know the dogfood version of Windows Live Messenger (WLM) 8 is floating around the net. This version is for internal testing for Microsoft employees. (dogfood means the company beta tests their own product before releasing it to Microsoft / MSN's beta testers.) You cannot login to WLM, unless you have a passport (www.passport.com) account that is set by Microsoft / MSN as a WLM 8 beta account.
There are programs out there to work around this, but there are known reports that some have viruses in them. I suggest waiting till the official beta starts. This way you get a more stable version, and not be possibly infected with viruses, Trojans and such.
I know a lot of you, like me are anxious to start testing WLM8, but I for one am waiting to be invited into the beta.
The first people to test it will be (us,) the MSN Beta Butterflies. We will then be able to invite our friends so we can test WLM 8 with out friends. Then more invites to follow. This info was pulled from: http://spaces.msn.com/members/MessengerSays/Blog/cns!1pa8Iikfy0xU3xf4W911Jq4Q!323.entry