> if I have it connect to 192.168.x.x isn't that just a common address that all routers share
No. 192.168.x.x. is what's known as a private class network - a special set of IP addresses that are not (normally) public - they're always local and usually behind some kind of gateway/router that uses NAT to translate the addresses into a real-world, public IP address.
That's why when you're at home your machine might have an internal address 192.169.1.2 but when you try to access a remote site, the router translates that address into the real-world public address assigned by your ISP, which is what the remote sites sees. When the remote site replies, the router remembers who initiated that connection and relays the response back to your machine.
In this way you can have multiple machines in your private 192.168.x.x network that all share a single public IP address.
>Also, it asks for a single address to connect to, and since the internal/private network is served out using DHCP, with multiple addresses being served, how do I list a single address?
I think you're getting confused with how the IP addresses on the VPN work.
In most cases your VPN server should have TWO addresses. A public address (let's say 65.43.2.1) and a private address (let's say 192.168.100.1).
In addition to that, the VPN server is told to reserve a block of additional IP addresses in the internal network to be used for VPN clients - let's say 192.168.100.101 through 192.168.10.110).
Now, when your client connects from home, you connect to the public address of the server (65.43.2.1). When the connection is established, the VPN server hands you one of the IP addresses from its pool (192.168.100.101 through 192.168.100.110), and it tells the client what address it's been assigned.
Now your client can try to hit anything on the 192.168.110.x network, including any printers, file servers, web sites, etc. in the internal network at the office. Your client will encrypt the connection and send it over the VPN where the VPN server will decrypt it and pass it on to the target server.
As far as the target server is concerned, the connection comes from the 192.168.100.x address assigned by the VPN server, so that's where it sends the reply, where the VPN server picks it up, encrypts it and sends it back down the tunnel.
That's the important part here. Because the VPN server assigns you an address in the internal network, all internal servers think you're local and know how to get traffic back to you. They don't know you're remote.
That's why you have to connect to the internal address of the server you're trying to connect to.
Now, as for the internal network using DHCP, that's the primary reason why you should always assign servers a STATIC IP address in the corporate network, so that you KNOW your file server is at 192.168.100.5, your printer is at 192.168.100.76 and your intranet web server is at 192.168.100.212 (or whatever). Of course, you should be using DNS to give this devices 'friendly' names that humans can remember, but the point is they should be static.
It's incrediably difficult to connect to a machine over the VPN if you don't know it's IP address/hostname, so don't waste your time trying to connect to a DHCP client. There are ways of doing it using DynamicDNS where the internal DNS server is tied to the DHCP server, so each time some device is handed an address from the DHCP server it updates the DNS tables, but it's non-trivial to setup.
