Windows Sharepoint Services (WSS) has an option which allows you to view the usage reports of WSS site.
Im my Project Server 2003 (PS2003) environment, I integrated my Public Document Site (WSS site) with my PWA interface. After some time I wanted to find out how many users are using wss site, which area is popular among my users etc.
There is a simple way to configure the usage analysis of site in WSS. Check these links for details.
After configurations, wait for the Processing Time to occur. Once done you will be able to see the site usage reports. For all details check those two articles.