Are you referring to the built-in Windows remote access? If so, you can disable Windows built-in remote access to your machine by:
Start>Run>Type sysdm.cpl>Click Remote tab>Uncheck Allow Remote Assistance connections to be sent to this computer>Click Apply
If you are referring to specific remote control software other than RDP... A good firewall would prevent unauthorized access, like ZoneAlarm including the free version, but you must specify during install that you want to manually allow/block programs. The option to automatically create firewall rules for certified Microsoft software could allow unauthorized access to your machine through some VNC programs since the one you have installed might be on the certified apps list. It's a good idea to have a firewall installed on the system anyway, whether you have a router with firewall capabilities on your network already. ZoneAlarm is what I use. It's the free version but in comparison to the other free firewalls, ZA is my favorite and has important features to keep your system safe from threats that even many paid firewalls are lacking.
Edited by astracner, 08 January 2011 - 02:41 PM.