Internal IP address visible

Hey there. I have a server running NT 4 with three nic cards. One is just a 3com, and the other two are the intel team adapters configured with the same IP address.
After capturing the packets sent from a client using our software to the server, we found that we are sending both our internal and external IP addresses to the client. How can I hide this internal IP address without messing up it’s connection to our internal network?