I recently took a business trip and, thankfully, the hotel had wireless internet available. After finding their network, connecting and getting an IP address, I opened Internet Explorer. Instead of my default page being loaded, I was directed to the hotel's page for their wireless access. It had information about their service, and a user agreement. Only after I agreed to their terms could I freely browse the internet.
My question is how did they do that? Is that a function of their access points, or is is special software on their server?