Google seem set to completely dominate the online world with their great software. This is the best way I've seen to keep track of the useage of your web site and it's completely free.
To make this work you need to do two things.
First go to the google web site http://www.google.com/analytics/ and sign up for an account.
Secondly you will need to include the code they give you in each page of your web site. If you use Joomla (1.0.13) this could hardly be easier. Simply add this mambot to your website and set the code