To enhance security, SQL Server 2005 Express Edition Developer Edition and Evaluation Edition install with only limited network connectivity. Connections to the Database Engine can be made from tools that are running on the same computer, but not from other computers. If you are planning to do your development work on the same computer as the Database Engine, you are finished. Management Studio or Management Studio Express Edition will connect to the Database Engine by using the shared memory protocol. This protocol is already enabled.
If you plan to connect to the Database Engine from another computer, you must enable a protocol, such as TCP/IP.
Start SQL Server Surface Area Configuration, and click Surface Area Configuration for Services and Connections.
In the Surface Area Configuration for Services and Connections box, the View by Instance box lists the instances of the Database Engine that are installed on the computer. The default instance (an unnamed instance) is listed as MSSQLSERVER. If you installed a named instance, the name you provided is listed. SQL Server 2005 Express Edition installs as SQLEXPRESS, unless you changed the name during setup. In the View by Instance box, expand the instance that you want to configure, expand Database Engine, and then click Remote Connections.
Click Local and remote connections, click Using TCP/IP only, then click OK and close the tool.