Are there any prebuilt modules for this? Is there an event thats called everytime a page is loaded? I'm just trying to secure one of my more important admin sections.
As blowdart said, simple IP Address logging is handled by IIS already. Simply right-click on the Website in Internet Information Services (IIS) Manager tool, go to the Web Site tab, and check the Enable Logging box. You can customize what information is logged also.
If you want to restrict the site or even a folder of the site to specific IP's, just go to the IIS Site or Folder properties that you want to protect in the IIS Manager, right click and select Properties. Choose the Directory Security tab. In the middle you should see the "IP Addresses and domain name restrictions. This will be where you can setup which IP's to block or allow.
If you want to do this programatically in the code-behind of ASP.Net, you could use the page preinit event.