I suggest learning about HTTP and DNS first. The easiest starting point might be to install firebug so that you can see what's really happening between a browse

I suggest learning about HTTP and DNS first. The easiest starting point might be to install firebug so that you can see what's really happening between a browser and a web server. In short, when the server receives the raw request, the targeted domain name and path are included in the headers. With that raw request its pretty easy to do whatever they need. Honestly, I dont really know what virtual hosts or rewrite rules are. These sound like specific features of web frameworks rather than anything inherent about the internet. Feel free to ask me questions by email. Also don't be afraid to say if you want to implement something similar. It isn't hard to do.