experts: how secure is my network?

Hi.

I’m the network administrator of a 28-computer NT network. We’re on DSL, with a Netopia router w/ built-in firewall. We don’t currently have anyone conneting remotely, but I’d like to set up a VPN in the near future.

I don’t know enough about security to figure out how vulnerable my network is right now — though I imagine that since I don’t know, it’s probably in danger. I also don’t know what the security risks of setting up a VPN are. I’m interested in securing the network, but I don’t know where to begin.

Insight, anyone?