Allow Internet access through server without network authentication

I want to allow guests to have wireless access to the internet through the same device employees will access the internet and authenticate to the network.

As it is now, you can access the network and internet when logged on as an authenticated user, but if you are not a member of the network you can connect to the wireless, but do not have internet access.

I could bypass the server by connecting the wireless directly to the ISP's router, but then network users would not have access.