Windows 7/2 Networks/One dedicated for PBX

I have done quite a bit of searching for the use of two networks in Windows 7. The majority of the posts are users trying to get Windows 7 to use both networks for all traffic. The situation I have here is that I have 2 networks. Network #1 is a cable internet service used for all internet traffic. Network #2 is a T1 PRI used for phone traffic only. The system we are using is an Avaya IP Office. The computer I'm going to have an issue with is the receptionist station. I need to hook both networks into their computer. So that the receptionist software will work, but i need her to be able to use the internet using the cable connection. I haven't set the IP Office up yet but I will be in the next couple weeks. I need to make sure i have everything ready to go. Any thoughts on how I can accomplish this or what I need to accomplish this? Any help would be great.