Express Manager has been terminated. SQL Server 2005 Express Edition will not ship with a management tool, initially. You can some information about its replacement in Paul Flessner's letter, and until as late as mid-2006 when this tool ships, you will still be able to manage Express Edition using Management Studio from other editions, Visual Studio, and a host of other applications (see this article for a more verbose list, though keep in mind that not all products have been updated for SQL Server 2005).