Hi,
For some reason, the link didn't work for me. But I'll try to clarify (it is confusing; I wish it weren't...)
ArcSDE for SQL Server Express is a name used for what are called Database Servers in the Catalog tree UI. If you have ArcGIS Server Workgroup, ArcGIS Desktop (ArcEditor or ArcInfo), or ArcGIS Engine, you can install SQL Server Express and run the ArcSDE for SQL Server Express wizard to register the SQL Server Express instance as a database server. Then you can connect to the database server/SQL Server Express instance, create geodatabases, add users, load/create data, and manage the database server and geodatabases all from the Catalog tree in ArcGIS Desktop. If you have ArcGIS Server Workgroup, you can also publish services using geodatabases on the database server as sources. (In older documentation, posts, and articles, you would have seen these geodatabases referred to as ArcSDE workgroup geodatabases and the ones licensed with ArcGIS Desktop as ArcSDE personal geodatabases.)
If you have ArcGIS Server Enterprise, you can install ArcSDE and use it with SQL Server Express. In that case, ArcGIS considers SQL Server Express as just another edition of SQL Server, like Enterprise or Standard. There are functionality differences and limitations that Microsoft has in place for Express, but it doesn't affect how you create, manage, and interact with enterprise geodatabases using ArcGIS software.
Let me know if further clarification is needed.
-Kim
