You have Vista SP1 installed. Windows Home Server misreports SP1 as Longhorn. That will get fixed in Power Pack 1.
Last year I purchased a Area-51 M5550. A few weeks ago I started getting a message to backup my data because Windows was about to expire. After two long sessions at Tech Support, I was told I would have to re-install everything or I could Microsoft and see if they could help me. In short, it ended with a complete rebuild of my system. So what's up with that? I should have known there were problems when ERD Commander and Windows Home Server reported in a Longhorn while other machines reported as Vista. Should companies be shipping beta OS's??? I am curious if anyone had this issue?