Rick,
It's some time since I did the Nagios thing - I was more involved with it's predecessor

Anyhow, you should be to check for a top-level index.html file (or index.htm if it's windows) as per the nagios docs.
That should prove the website is up.
Damian
BTW - I've just had a look at the current nagios documentation and it's appalling. Based on the website, I can't see why you chose it. It used to be a be an excellent tool for service monitoring - we replaced Big Brother with Nagios at one site when BB went commercial. I can't say now that we'd do the same based on a look at the website.
I'm going to have a word with Mr Galstad.