Although I was aware of the surface area configuration tool for SQL Server but honestly I never used it. In a scenario where I had two VMs running on Windows 7 host OS, one with AX2009 AOS, client etc installed while the other VM only had SQL Server 2005 on it. The goal was to let AOS communicate with SQL in this virtual environment. Using the configuration tool on SQL VM, I was able to do this by allowing remote connections to this SQL from the AOS VM. Take a look at this KB article from MS:
For SQL 2008, the tool has been taken away and I believe the SQL Server Configuration Manager now takes care of remote connectivity.