You might be interested to know that almost the entirety of Sierra's Online Network (The Sierra Network, later known as The ImagiNation Network) was run through a SCI engine. The exceptions to this were, of course, the stand-alone games such as Yserbius, FrontPage Sports, and Red Baron.
No, SCI does not include networking... however, the INN SCI engine *did*.
Unfortunatly, the resources for INN were encrypted using a different key than most SCI games, so you'll need some luck getting into the scripts that would reference the network libraries.