I'm trying to set up one computer, XP Pro 2 NICs, to connect to 2 totally different networks. One network (172.x.x.x) is setup accessing the wan via T1. Second network is local (192.x.x.x), however is used to connect to the internet and email. The problem I'm having.. When I setup the 192.x.x.x NIC with DSL modem gateway, the 172.x.x.x side will not connect via T1 to mainframe. The 192 NIC will connect to ISP, website and email no problem. Remove the 192 gateway and the 172 connects, but of course I can't connect with the 192 NIC.. Can this be done?

Yes. The problem you are likely experiencing is the use of two gateway addresses. So here is a way to solve this.

Write down a list of all of the network ID's located on the WAN.
Delete the gateway address from the 172.x.x.x network adapter, keeping only the gateway address for the router on the 192.x.x.x adapter that is connected to the Internet. The gateway address for this adapter should be your Internet router.

As an example, we will assume that you have two network ID's on your LAN. They will be 172.16.x.x and 172.17.x.x. and we will assume that your NIC that is connected to the 172.x.x.x network has the address 172.16.2.20 and it is a Class B subnet. We will also assume that your WAN has a router with the LAN address 172.16.1.1 and it is also a Class B subnet.

Go to a command prompt and add the following persistent routes:
route add -p 172.16.0.0 mask 255.255.0.0 172.16.1.1
route add -p 172.17.0.0 mask 255.255.0.0 172.16.1.1

You have now defined the exceptions for your 192.x.x.x gateway address. You are saying that you want to use the 192.x.x.x gateway address for ALL requests EXCEPT anything that is addressed to the 172.16.x.x and 172.17.x.x Class B networks and you want them to be routed through the 172.16.1.1 address. Your NIC that has the address 172.16.2.20 is capable of connecting to this router because they are on the same network ID.