Microsoft has released the beta documentation for both of the following products that are currently under development.
Windows Based Hosting for Applications 1.5 is for ISV's that want's to enable their solutions for Hosting (Download).
Windows Based Hosting 4.5 (Download) contains the following updates to WBH 4.0
Windows Server 2003 R2
The infrastructure components of the solution now run on Windows Server 2003 R2, which extends the Windows Server 2003 operating system in important ways. Web platform features include support for .NET framework 2.0 and ASP.NET 2.0 applications as well as 64-bit support for Internet Information Services (IIS) 6.0.
A new licensing model that allows customers to get more value out of server virtualization.
SQL Server 2005
The solution incorporates fundamental advancements in database technology and security with SQL Server 2005. When compared with SQL Server 2000, the latest version of the comprehensive database platform of the solution provides:New features to easily support service offerings differentiated by additional capabilities rather than just database size and quantity.Support for 64-bit platforms so service providers can scale servers to any client's needs.
SQL Server Hosting Toolkit
This tool enables hosters to more easily deploy SQL Server databases for customers.
ASP.NET 2.0 support
ASP.NET 2.0 encapsulates common Web tasks into application services and controls that you can easily reuse across Web sites. With these basic building blocks, ASP.NET 2.0 allows developers to write up to 70 percent less code for faster development of rich Web sites and applications.
ASP.NET AJAX framework support
Hosters can now offer developers a richer environment on which to build interaction-rich, cross-browser Web applications.
Support for 64-bit computing
As the majority of new server shipments today contain 64-bit processing power, the solution has also moved forward with 64-bit computing support. The solution has been tested with and supports 64-bit versions of Windows Server 2003 R2 and SQL Server 2005.
Support for Windows SharePoint Service version 3.0
This version introduces improved administrative tools including a server farm-based Central Administration user interface. Also new in this release are the availability of 40 new application templates which hosters can use to enhance service offerings for small to medium business customers.
Source - Windows Based Hosting 4.5 beta documentation.