I am very very new to this technology so please bear me out with the simple questions. 
I have a network all ready set up which is SBS 2003 and a 2 nic setup, an ADSL Netgear modem/router/firewall.
I now need to have a link to another company in order to access their systems.
I have installed a 64k diginet line at my site and at the other site.
I have purchased 2 x 1841 Ciso routers one for me one for the other site.
I now need to setup and connect the two together and thats where it becomes grey and blurry.
The 1841 has a serial port connected to the NTU.
The other company has given me their ip address that my router on their side will connect to and told me 
to setup the router first and then ship it down to them.

So I need to know what needs to be done this side from IP addressing and Ethernet and serial setup. 
The router also needs to NAT.

This is what info I have so far, I need to know what type of IP address range and subnets I should be using

My Company
**********
Ethernet Switch		Netgear		Cisco
192.168.16.x		172.168.16.x	Eth0 xxx.xxx.xxx
					Ser0 xxx.xxx.xxx
External Company
****************
Ethernet Switch		Cisco
192.168.17.x		Eth0 xxx.xxx.xxx
			Ser0 xxx.xxx.xxx