The offical word on this topic is as follows:

With the launch of Windows Server 2008, SQL Server 2008 and Visual Studio 2008 right around the corner, a number of you have asked when you will be able to take advantage of the new platforms with BizTalk Server.  We are currently investigating various options to deliver updates prior to Oslo. As we have done historically, this would follow the RTM of Windows Server and SQL Server.  This will give us time to do the final work and testing to ensure compatibility.  Our intent is to provide an integrated release that supports the updated Tools (Visual Studio 2008), OS (Windows Server 2008) and DB (SQL Server 2008) as part of an infrastructure update.

As soon as we finalize plans, we will update the community.  This should hopefully happen sometime during this Q1 CY 2008 as the planning work is still underway.

This does not give much away, however it does center around a bunch of work on Oslo.. so watch this space.