Two NIC card setup - need help

Hello,
I have two windows servers (2003 and 2008) on two different routers/networks that I do need to connect between each other. Both of the servers have two NIC cards. I got a crossover cable and set up a new network on a totally different IP addresses so they could see each other, but after that one of the servers got "confused" and as far as I could tell - tried to access that new network for an internet connection and so I needed to disable one of the cards to get it back to the proper functioning.
So, the question is - how i can prioritize (???) first network to be the only network for an internet access, and second network - only for manual file transfers (I need to transfer backup files via that one). Sorry for kinda stupid explanation, but I hope that it does make some sense....
Thanks!