http://www.microsoft.com/downloads/details.aspx?familyid=39ebef74-1c29-49fe-8221-c94f2b52f6c6&displaylang=en
and Express edition
http://www.microsoft.com/downloads/details.aspx?familyid=57856cdd-da9b-4ad0-9a8a-f193ae8410ad&displaylang=en
more info here
http://blogs.msdn.com/sqlexpress/archive/2006/03/16/Express_CTP.aspx
This service pack was always expected - MS posted a TPC entry with SQL 2005 at the end of last year.
http://www.noelwatson.com/blog/PermaLink,guid,82af9e3b-d08f-4b2b-85fc-9797aa55a567.aspx
MS are now moving away from traditional betas and releasing more frequent CTP's. It's good to see MS improving the functionality of their free offering.