We started on Comcast cable. We also installed DSL Verizon to compare them. Currently we have both services into the house. Problem is, once a computer has been set to connect to the DSL modem, it cannot acquire a network address from the cable modem.

Previously, I successfully set up internet access through the cable modem, both hardwired and wireless

Then I disconnected from the cable modem and successfully set up the internet access through the DSL modem. It required me to install Verizon software

Here is the problem:
Now I disconnect the cat 5 from the DSL modem and connect it to the cable modem. I cannot acquire a network address.

I think the Verison software has made some changes that prevent acquiring a dynamic network address from the Comcast cable modem.

What settings might I need to change to acquire the cable modem address, and where would I look for it?

Verizon - Westell 6100 DSL modem
Comcast - Motorola SB5120 cable modem

two computers, both running Windows XP os