Web Crawler

Question

Has anyone done anything like the following or has any ideas how I could go about developing it. I'd like to come up with a competitor analysis tool that basically checks for new content on specified URLs at specific time intervals (days rather than minutes or hours). If there are any changes then these should be email as attachments to an email. The difficult bit as far as I'm concerned is ensuring that only changes in the main content cause an action and not just a different advert on a page! I envisage that this will be a console or perhaps windows form application. Any help would be appreciated. DJ