Welcome to WebmasterWorld Guest from 220.127.116.11
Log files, report, accurately, requests to the http server. And that is ALL.
In simple terms, most companies use a router between their LAN and the Internet. So while every work station in the company has its own IP address, this IP address is local. To the Internet, all stations go through a single router with its own, single IP address, presenting to destination web sites requests (if they get that far and don't get handled by ISP caches along the way) of requests made by a single IP address, which many misleading packages reveal as a single user.
With complex cookies you can do some tracking of run-of-the-mill users, but technicaly savvy users may disable cookies or even delete them during a session, so again results are not to be relied upon.
Read the library thread [webmasterworld.com...] for more info.