How do they do it? Hotel automatically routes me to a webpage when I log on

I was recently at a hotel in Texas and had my laptop with me (wireless card installed). I simply turned on my laptop, I saw the network on my list of available networks, make the connection (no password req'd). Once the connection was made, my browser opened automatically and a webpage specific to that hotel was loaded.

How did they do that?

I would like to install a similar service at my place of business. I have a Linksys WRT54G wireless router that is connected to the internet. I would like guests to come to my site, locate my network and be able to log on automatically to the web. How do I get there from here?

 

One way to achieve such a setting is to install Windows 2003 with IAS server, and set it for Unauthenticated Access.