2 Networks on Same Machine

I have a Win 2000 Pro PC with 2 NIC cards and I am trying to connect to 2 separate networks. Both have static IP addresses. Network A has high speed internet available, Network B does not. Network A uses the IP address format 192.1.1.X, wile Network B uses 10.152.6.X, Subnet mask is same for both 255.255.255.0. Both have different Default Gateways and different DNS Servers.
I can’t get both to work at the same time. One works when I disable the other and vice versa.
Is there any way to be able to connect to both networks simultaneously??
Thanks much.