Network access to the service is deactivated by default. In order to allow access to the server from the clients, you need to activate TCP/IP. Go to START -> Microsoft SQL Server 2008 -> Configuration Tools -> SQL Server Configuration, then hit Network configuration and activate TCP/IP. Restart the SQL Server for the settings to take effect.
Also, please doouble check, if your SQL Browser is running. This allows you to see the Server in your drop down list in XTAdmin.exe.
Download the Xpert-Timer Setup from Xpert-Design Software website:
Start the setup. You'll be guided through the steps. After you've finished the installation, start up XTAdmin.exe if it doesn't start automatically. Now you can create your new database.
If the connection to the server was successful, you can now "Add a new database".
If you have multiple users working with Xpert-Timer, remember to install the xperttimer.exe on a network drive, so all users only work with one .exe. This way it's easier to install updates of the software.