Detection of uniques will entirely depend on your CPM provider. They can provide 24-hours unique...or 1 week unique...etc....but it depends on the provider's software settings.
CPM is defined as cost per thousand impressions of a banner or ad unit. So say you are getting a $5 CPM rate you would make $5 every time a banner is displayed on your site.
Actually, it works like this for the above example: The advertising site will show 1000 ad impressions to site visitors for a total cost of $5.
i was approved at http://www.valueclick.com/ at the time i didint know much about advertising apparently my account is still there with a site that's long gone, i just sent in a request for approval for my new site on the account. valueclick.com is good what i hear, right ?