Is there any way to install SQL Express 2005 silently while configuring to allow remote access, or must the configuration be done with the SQL Server Management Studio UI?
After the SQL Service is installed log into the database and run the following and then restart the SQL Service.
exec sp_configure 'remote access', 1
reconfigure
This will allow remote access to the service. If you are installing a named instance you'll need to ensure that the SQL Browser service is running and set to automatic.