If your ISP permits, you can prevent the external IP address from changing on the router by assigning a static IP address to the device in the Linksys router administrative interface.

If so, how do I configure the router to connect to the cable modem? Normally I can choose DHCP, PPPoE, etc, but I'm not sure how it will work with multiple external ip addresses. Thanks for any help!

This short tutorial walks you through the process of changing a CentOS ethernet interface from DHCP to static--but be prepared to type.

How do I tell XP Pro to use my router on 10.0.0.138 to assign its DHCP IP ???? rather than DHCP 255.255.255.255 ?