Any computer within your network that is connected to the Internet, directly or indirectly, is a potential risk for an attack from viruses or external attackers. Traditionally, firewalls provide defense against such attacks. Towards this end, you should review your firewall deployments to ensure that the current rules and processes to implement and maintain them are still valid. You should also make sure that you take adequate measures to help protect devices such as laptops with technologies such as host-based firewalls.
A few final thoughts you should consider include making sure you have secured your wireless network to help prevent unauthorized users from gaining access to your network resources. You should also consider upgrading all Internet-facing servers to Microsoft Windows Server 2003 and all traveling laptops to Windows XP to take advantage of the reduced attack surface of these products, as well as to utilize the additional security features such as Windows firewall for these high risk devices. Finally, you should consider using IPSec to help prevent unauthorized users from gaining access to mission-critical resources or rogue machines from accessing your network.