Help Me understand my network

I am starting into networking.
Getting really confused about my network.
I will best explain to you about my network please help me whether my understanding is correct.
I am not sure but I guess the setup of our network is like this.

T1 Line Internet - Cisco Router - PIX Firewall - Hub - W2k server and clients

Our internal LAN has 10.x.x.x addresses and DHCP enabled.

On an internal network machine when I do ipconfig it is

DHCP enabled - DHCP server is our w2k server (10.x.x.x address)
Default gateway - a 10.x. (this IP is same as our firewall)
DNS server - a 10.x ip address (this is our w2k server)

Also w2k server has 2 NIC's.
When I access the PIX firewall using the web I see something called interfaces and there are 2 entries one says outside and has some different IP address I guess this is static IP from our ISP and one says inside which shows our 10.x..address.

-Could some one tell me whats the structure of our network.
-Why we have 2 NIC's
-why is the firewall showing the default gateway.
-How is the router configured.?
-Where do I find my DNS servers (ip addresses provided by our ISP)

The need for me right now is. We have a new T1 installed and planning to switch our current T1 line.The new T1 folks say I need to modify something (they have given some Ip addresses) so that I can use the new T1 line. I do not know where to modify it. I can really give more information.

Why we have 2 NIC's
answer: most servers come with two nics for adapter teaming by default anymore. You can not do adapter teaming with a hub. Disconnect and disable one nic.

-why is the firewall showing the default gateway.
answer: you firewall IS your gateway. In other words its the guard dog between you and the internet. Where would you expect your guard dog to stand? Certainly not behind you :-)

-How is the router configured.?
answer: if you don't know this then hire a contractor who does.

-Where do I find my DNS servers (ip addresses provided by our ISP)
answer: I don't have a clue what you are asking.

You would modify the wan port settings on the Cisco router with the ip setting provided by the ISP.

Hire a local Cisco router person!!! This is NOT something you should attempt to do yourself!!!! Or better yet hire/make the ISP do the configuration for you. They should know how.

As wanderer2 said that the firewall is your protection from the outside but the router will be your gateway.The router will have an IP address and this is your gateway, put this in the setting that says gateway when configuring the server and if you are using the server to route for the client pc's then the servers IP address will go in the settings for each client pc. I am assuming you want the server to handle that. As far as the Cisco router, they are not your average do it yourself router as wanderer2 already tried to say, unless you are talking about a linksys router made by Cisco, this I think you can handle, most have a nice gui to work with. ANyway try looking at the cisco website foir help configing that. If your not in a rush just take your time and you will get it As far as your DNS settings you mean DNS servers at the ISP, that T1 goes to a server somewhere down the line and at that end is domain name server (DNS) that does the name resolution for the internet translates www.younetwork.com to 204.12.10.1... you get the picture. Anyway you need to call and ask your ISP for that.