You need more answers. I'm not sure you want to disallow remote access.
The link below will give you a lot of information on remote access.
http://www.windowsecurity.com/articles/Securing_Remote_Access_Connections.html
This information is from WindowsXP Help:
Remote Access Authentication Process
When you connect to the Internet, remote access authentication is a one-step process. Your computer presents credentials, typically a user name and password, that are acceptable to a remote access server at the Internet Service Provider (ISP), and you are granted a connection to the Internet.
When you connect to a corporate network that uses a Windows domain, a similar remote access authentication occurs. But in this case, a second step of authentication is required. After you have connected to the network, resources that you access, such as file and print servers, will ask your computer for its domain credentials on each attempt to access them. These domain network credentials may not be the same as the credentials required by the remote access server.
In addition, computers running a secure operating system such as Windows XP require logon credentials in order to allow the user access to the computer itself.
This means that your computer could require three sets of credentials for remote access: one to log on to the computer itself; one to satisfy the remote access server; and a third to handle challenges from resources on the network. These credentials can be the same, as described below, but they can also be different.
Corporate computers on secured networks are typically members of the domain. In Windows XP this means that the credentials the user presents when logging on to the computer are verified against the domain controller before granting the user access to the computer. As a result, these are the same credentials needed to satisfy network resources. To simplify remote access, many corporate networks are arranged so that the remote access server will also accept the same domain credentials. This allows a single logon for member computers of a domain. One set of credentials unlocks your computer, provides remote access to the corporate network, and allows access to network resources once the connection is established.
To assist in the single-credential case for computers that are members of a domain, network connections in Windows XP can be configured to present the user's logon credentials to the remote access server. This eliminates the need to supply explicit credentials for the remote access server. Since the logon credentials are the same as the user's domain credentials, the same credentials satisfy resource challenges from the network.
However, computers outside the workplace (such as home computers), are generally not members of a domain, so the user logon credentials that unlock the computer do not provide access to the domain. There are also cases in which a remote access server requires credentials that are independent of the network domain's credentials. In this scenario, you would have to provide three different credentials in order to log on to the computer, connect to the remote network, and then access resources on that network.