Open wireless with Proxy Server

Hello.

I want to use my W2K3 Server as a wireless server.
The box will have:

1x Wireless NIC for LAN
1x NIC for LAN
1x NIC connected to modem for internet

I want my wireless network to be unsecure (so anyone can connect) but i dont
want them to be able to access the internet, will i have to use a proxy?

I also dont want them to be able to see computers on the network so they
cant access file shares etc, VPN?

What would be the easiest way to achieve this? I would like to use free
software if possible.