Built into Windows Server 2003 is the ability to suppress a specific IP address from accessing any web site hosted through Internet Information Services (IIS). This ability is useful for instances such as banning a particular user from a forums site, or blocking a suspected fraudulent customer from accessing an online store.

Navigate to Start à Administrative Tools à Internet Information Services (IIS) Manager.

Click the plus sign next to the Local Computer name, and then the plus sign next to the Web Sites folder.

Right-click on the web site you would like to block the specific IP for, and choose Properties.

Once the Properties screen is open, click on the Directory Security tab and then click the button which says Edit under the IP address and domain name restrictions.

Leave the option of Granted Access selected, and choose Add.

Enter the IP address of the computer you wish to deny access to. Leave the option for Single Computer selected. Once entered, click OK.

You should now see the IP address in question listed, with Denied listed next to it. Click OK.

The specific IP address listed is now blocked from accessing the web site in question. Please be aware that this will only prevent the IP address from accessing the site it is blocked for, and not the server as a whole.