Question : VPN security - is the way I use VPN secure?

I have 4 pc in my network, all behind a linksys router. 1 pc has very important files and it use VPN to transmit data. I installed firewall and anti-virus on that pc. So is this pc secure enough when doing VPN transmission? what's the best way of setting this pc?

Answer : VPN security - is the way I use VPN secure?

Software firewall is a good option.

Is this a (a) site to site VPN or a (b)software client to site VPN?
(a) you can specify with a site to site VPN which PC's can use the tunnel with IP addressing restrictions or ACLs (access control lists)
(b) with a software VPN, usually split tunneling is disabled by default. If this is the case access to the local network is blocked, much like a firewall would do, while the VPN is connected. Split tunneling is managed in different ways with different VPN's. What are you using? If the Windows VPN client go to:
control panel | network connections | right click on the VPN/Virtual adapter and choose properties | Networking | TCP/IP -properties | Advanced | General | make sure you check the box  "Use default gateway on remote network"