HBO Television Distribution is obtaining the rights to distribute the show, but that doesn't mean it will be shown on the HBO channel. That's the misconception that people have been getting.
When Lifetime's contract for UM ends in 2008, that will mark the end of Buena Vista's status as the distributor forthe series(hence HBO Television Distribution's announced acquisition of the show). Unsolved Mysteries is being shopped around to other cable networks, as indicated in a recent article at the Broadcasting & Cable web site.
http://www.broadcastingcable.com/article/CA6454846.html
Because the expiration of Lifetime's deal with UM is a year away, I expect that it will be many months before any or all deals related to the proposed UM revival are finalized. Projects like this take time, so I wouldn't be alarmed if no deals (new host, new network, etc.) are reached before the end of this year.
Stay tuned.