you're looking to enable dual homing windows 7 (that's your google terms)
»
windows.microsoft.com/is ··· -networkseems promising
or possibly
»
www.eightforums.com/tuto ··· ers.html (tip for windows 8, but a win 7 user posted it worked for him too...)
As a last resort, you could also make a Virtual machine that is connected to the alternate network's adapter ONLY, then the VM would be on that network, while the host is on your primary network.