If you're referring to the IIS web server logs, they're located at c:\WINDOWS\system32\LogFiles\W3SVC1 on your server. You can actually use Crystal Reports to report off of these files using the "MS IIS/Proxy Log Files" connection type.
The IIS logs are not terribly useful, but you can obtain some general information about the activity level of your servers and the number of distinct users at various times.