[CentOS] Networking help

I have a centos 4.0 box that has three network interfaces and is used as router. It runs shorewall as a two-ISP firewall for a single LAN. This morning, the motherboard's LAN interface gave trouble, spewing out IRQ problems, so I disabled it and changed the network cards. As I only had two slots, I tried a dual NIC card, but it crashed the system every time. Right now I am trying to fit two single NOCs in and to bring the machine back up. However, I can;t get any traffic to route. The DHCP ADSL card will not get an IP. I have used Kudzu to configure the new cards, turned off Shorewall, but no matter what I do, teh cards can't talk to the WAN or LAN. The ADSL is fine, my laptop gets and IP easily. Any ideas what I need to look for?