OK, the problem is that I am trying to configure two SQL Server 2005 machines to communiacte over two subnets so obviously a router is sitting in the middle. When I run osql -L there are no SQL Servers in the second subnet listed and so my first thought was that traffic was being blocked at the router. Unfortunately it is not that simple!
I have done the following on both ends of the proposed connection:
1. I have used the Configuration manager to ensure that TCP/IP is enabled
2. In the Surface Area Configuration Manager I have ensured that Remote Conections are allowed.
3. At the instance level in the Server Properties under Connections, "Allow Remote Connections to this Server" has been checked.
I can PING the target router to see that it is alive but SQL Server itself cannot see the other instance.
I would be grateful for any help you can offer!