Editing sample from version 2.0 of the javascript api - for this a Feature Layer service is required where the Feature access is checked on the service and data residing on ArSDE single geodatase. My question here would be if this single ArcSDE geodatabase can be an ArcSDE installed with the SQL Server 2008 express edition. I have tried the express edition that only let me create a dbo based schema for the database and I'm not sure if the ArcSDE geodatabase required for the Feature Accesss can be a dbo based schema geodatabase.
Yes, you can do this. I currently use this set up as my development environment. More specifically, it's a workgroup ArcSDE GDB stored in a SQL Server 2008 Express instance.