You would need a static (in, out) mssql-out mssql-in netmask 255.255.255.255 to allow the mssql server to be seen by the iis. The -out is the ip of mssql as seen by iis, the -in is the actual/real address of the mssql. The -out and the -in values can be the same.
You then need to configure an access-list and apply it to the outside interface to allow the iis to connect to the mssql server. By default mssql runs on tcp port 1433, but the newer versions have virtual hosting that requires a udp connection to 1434 I believe. I don't know how you setup mssql, but to get the acl to work you need to know what protocols and ports iis is using.
