Error connecting to SQL Server 2008 Express over a LAN

We have a VB.NET application which uses SQL Server Express 2008. This application could have any number of users. One user will be the server, so there won't be any problem in connecting (.\SQlExpress). But other users have to access the database through LAN, where I couldn't connect. I have given \SQLExpress (should I try with the IP address of server?). I get an error. Why?

We are not giving them SSMS, only SQL Server Express.

Code used to connect is VB.NET.

By default, SQL Server express is not configured to allow for connections from other computers. In order to do this, you'll need to access the SQL Server configuration snap-in and enable TCP/IP connections. You'll also need to ensure that the firewall on that computer is configured to allow connections to SQL Server.