Echange/Proxy on BDC connection help

I have a BDC NT4 that has exchange 5.5, Proxy 2 installed I have just changed over from dialup to permanent connection. I have installed second nic into server and connected that to cisco switch. I have connected router also to switch and I am having problems now connecting to both that server and the internet. What am I doing wrong and what should I be aware of. On installing second card I recieved a message regarding default card address and did I want to change it ?? Please Help switch is set up fine!