Microsoft Wednesday christened its forthcoming server bundle for midsize businesses Windows Essential Business Server and said it would release a second beta by year-end and ship the software late in 2008.

The server bundle, which was code-named Centro, includes Windows Server 2008, Exchange Server 2007, Forefront Security for Exchange, System Center Essentials and the next version of ISA Server in the Standard Edition. A Premium Edition adds SQL Server 2008. All the software will be offered as part of a single 64-bit only server package.

The bundle, aimed at companies with 25 to 250 PCs, has been in the works for the past two years. It has mostly been hung up by delays in Windows Server 2008, which forms the foundation of the bundle, but it is also waiting on SQL Server 2008 and a new version of ISA Server.

Bill Gates, Microsoft’s chief software architect, first unveiled Centro during the company’s first ever Business Summit for mid-market companies in September 2005. The original target ship date set by Gates was 2007.

During the delay, Microsoft has unfolded its software-plus-services initiative and its plans to offer all its core software in a services model. Centro will be released as an on-premise product, but Microsoft officials say they will evaluate the services angles for mid-market customers.

“As the software-plus-services model evolves and as the core products of Windows Essential Business Server have service offerings we will look at including them,” says Russ Madlener, director of product planning for the Windows Server solutions group within Microsoft’s server and tools division.

Microsoft said Windows Essential Business Server (WEBS) will require only a single client access license (CAL) per user to access all the features of the bundle. The bundle also includes a management console that is extensible and Microsoft partners CA, Citrix, Full Armor, Symantec, and Trend Micro have already built add-ins for it.

The console also lets users manage the CALs for WEBS via the console, which reports how many licenses a company has and who they are assigned to. Administrators also can reassign CALs to other users.

Next week, at the company’s annual IT Forum in Barcelona, Microsoft is expected to demonstrate WEBS running on Intel hardware. Other hardware partners also are supporting WEBS, including Fujitsu-Siemens, HP and IBM.

Microsoft also said the next version of Windows Small Business Server, code-named Cougar, is in a private beta and that the road map for the software will be updated in the coming months.