Use ISA 2004 if you have SBS 2003 PremiumIf you already own the SBS 2003 Premium Edition, install and use ISA 2004 instead of relying on RRAS for your firewall.
Open ports only as neededOnly open ports that are really necessary; opening ports that are not required can put your network at risk.
Regularly test your firewallEvery once in a while get a port scanner and scan the external interface of your server.
Enable password policiesWeak or unchanging passwords are a security risk to your network, especially when remote access is enabled.
VPNs are not a panaceaThink twice before enabling inbound VPN access to your SBS network and consider all the security risks of doing so.
Practice safe VPNNever establish a VPN from a computer that is not under your control.