Actually, now that I think about it Steam checks for a login (SteamID) before you can even launch CS, even if its to play a single player.
To set it up, its basically the same way as CS 1.5 so when you create a game under a LAN, people should be able to see your game under their "LAN games" tab.
Try lauching the hlds.exe in your C:\Program Files\Steam\SteamApps\[email address]\counter-strike folder. But I don't know if there is a server.cfg file you need to go along with it. Google hlds.exe and 1.6, I'm sure you'll find what you're looking for.
Thats another reason i don't liek about steam.. u can't play LAN with ease.. half of my friends like gave up playin CS cuz steam was added.. its sad...