IIS Custom Error page and ColdFusion Url Rewrite question

Here's what I've done. I have a website setup that has only one physical page, index.cfm. All the links on that site are set up to be SEO friendly. Something like: domainname.com/my-coldfusion-question. I have set up a custom 404 page in IIS to include a coldfusion page called masterRewrite. When the page is called it parses the url, queries the database and builds a page that returns to the browser. So basically ANY link that one might go to on the site always returns a page with content and the browser never gets a "Page Not Found" error. So here's my question: When google spiders my page does it ever know that a 404 has occurred? I've tested a little bit myself by using cfhttp to go to a page that doesn't exist on the site and viewed the headers. The response header returned shows the same as a page that does actually exist. StatusCode is "200 OK." So my question is, does Google see this the same as a page that actually does exist? I originally thought that it did, but have noticed my page ranking is 0/10 and was wondering if somehow Google knows the difference despite the fact that the statuscode shows as 200. Any insight would be great, thanks. Michael