Help locking down access to client data from "outside" hacki

[grindy]

My situation is this:

I have a small business with 5 users. Each user can access our clients data from our internal file server. All users are running XP Professional, as is the server machine.

All of us require daily internet access, which is broadband cable behind a router. Each system is running a Security Suite with personal firewall.

What I need to do is be as certain as is "practically" possible that our clients data is not "compromised" from the outside ( via our broadband connection ).

What - if anything - should I add to this setup to be more secure from "outside" hacking?

All comments are certainly appreciated.

[Scarecrow Man]

First of all, do you have a domain?

If you do, it's quite easy to set up security measurements, and you only have to do it once. If not, it could be difficult, and would have to be done for each individual machine.