Microsoft is busy making sure the next version of Site Server (code-named "Olympus") is more integrated than the current scatter-brained version. As anyone who's played with Site Server can attest, the first version (oddly labeled "2.0") is simply a collection of tools from companies Microsoft bought in the previous year. There was absolutely no integration and each had a different, and separate, install program (imagine getting Microsoft Office and having each program have a separate install and you get the idea).
Olympus will include Internet Information Server (IIS) 4.0 which is itself in beta at this time. IIS 4.0 includes Transaction Server and Merchant Server. When Olympus is completed, it will be added to the BackOffice suite of server applications. BackOffice 4.0 is due later this year.
A pre-release version of Olympus will be made available to the public this Fall.