I've been trying to accomplish this for months, maybe years, and I've finally done it!
Well, it's not complete, but I have created a CGI application that will dynamically create a thumbnail of a whole web page. To better explain, if you typ in the URL to my program, and you give it the URL to some other site, it will create a gif image of that site to the size you specify. Perhaps an example image is a better explanation (see right).
You simply set the url, width and height parameters, and off it goes. Like this, for example:
http://www.asymptomatic.net/webthumb.exe?w=160&h=120&url=http://www.nytimes.com
That URL doesn't actually work because I'm still making changes to the code to get it perfect, and so I haven't put the application online, but on my desktop system it produces the gif image that appears with this article.
You may not recognize the significance of this feat, but I assure you, it's quite a good thing.