Is Virgin PC guard efficient enough to be used as the only firewall?

PCguard is only available to Virgin Broadband customers so I am not familiar with its effectiveness.

If you choose to use a 3rd-party firewall, you need to disable the Windows firewall. Using two software firewalls on a single computer could cause issues with connectivity to the Internet or other unexpected behavior. Further, running multiple software firewalls can cause conflicts that are hard to identify and troubleshoot. Only one of the firewalls can receive the packets over the network and process them. Sometimes you may even have a conflict that causes neither firewall to protect your connection. However, you can use a hardware firewall (your router) and a software firewall (Kerio or ZoneAlarm) in conjunction.