You can use Microsoft's LogParser. Refer to this article at SecurityFocus.com for gobs of information. To download: LogParser 2.0 (for Windows 2000) or LogParser 2.1 (part of the IIS 6.0 Resource Kit for Windows Server 2003).
If you're more of a do-it-yourself kind of admin, you can read this article by Mike Kayzer.
There are also several 3rd party components and statistical packages out there.