Securing SQL Server 2005 Express

Hello,


I developed a small desktop system using SQL Server 2005 Express as the data backend. The machine that hosts SQL Server 2005 Express, as well as all the workstations that interact with it, belong to the same private LAN segment. All of them have non-public IP addresses from class 192.168.0... which means they're not directly visible from the outside world, despite having internet access through a router that does NAT. As we all know this is the typical scenario for sharing internet access in a small LAN.

Now, my concern is with the security of the host running SQL Server 2005 Express. In particular, what measures do I have to implement to minimize the risk that may come from the public internet ? It's naive to think that because the potential attack surface is NATted behind a router, security is guaranteed and data theft or DoS attacks won't simply happen.
What are the guidelines for securing SQL Server 2005 Express in a scenario like this ?
(Side note: SQL Server 2005 Express is running on Windows XP Pro)


Thanks.

Fernando