Question : Cisco 1721 basics

I am new to Cisco routers and firewalls. I'd like to purchase a router to use for my network. I have been looking at a 1721 (I don't want anything newer, I can get a good deal on this one) with two T1WICs (Is there a difference in WIC and DSU?). I have a cable modem. I am unsure of how the WIC cards actually work. I know there are different speeds, but can they be used with a cable modem? The 1721 has an ethernet port, but only one.

Answer : Cisco 1721 basics

Opps, I mis-spoke, you can get  a  WIC-1ENET, which is a 10 Mbps Ethernet port that goes into one of the WAN slots.

So you buy the  WIC-1ENET, install it, connect your Cable Modem to this port and the 10/100 Mbps Ethernet port to your internal network.