Mike, is correct. If you are counting IP numbers, you will get a lower number than the number of people actually visiting your site. We use Webtrends but it is no where near perfect. Ours is not perfect either, since I'm actually missing the first month we were on as far as stats go. Let me check on the name for you.
Page views are the next measure and they count the number of HTML views throughout the whole site.
It is the most effective method of knowing what traffic your site is getting, but it won't tell you exactly how many people. We count IP's on each page and then compile a master list to see which pages are getting the most traffic. Counting IP nubmers will give you a lower bound and Page views will be your upper bound. Wusage is the program we're using. What I am looking for are trends.