If you want this for one site and want to see what’s shown to user in different browsers, then browsershots.org will be great for you. This service allows to take screenshots with different browser – this is the most comprehensive tool related to page screens I’ve seen on the Web.
There is also a Windows software that allows to do this. It’s Thumbnail Grabber. Thumbnail Grabber is a free utility for creating thumbnail screenshots of web pages in JPEG format. You can choose web page size (width and height) and thumbnail image size (in percent of the web page size). The program can batch process URLs and domains from a text file that makes it extremely useful for sites that have reviews or galleries, etc.
Now the process of Image creation is very simple. All you have to do is to have a list of web pages to crawl and Thumbnail Grabber will do everything for you. Nice that it doesn’t capture any browser elements, so your screenshots are clear and look great