Using Parallels Desktop to run Windows on a Mac for VoIP Softphone

We recently got a Shoretel VoIP system put in. Our general manager travels and works from home a lot. When he is not in the office, which is the majority of the time, he uses WiFi on his Macbook Pro to connect to the internet. In order for him to have a phone on our VoIP system he has to have a softphone. The softphone will only work in a windows enviroment so I installed Parallels to run Windows on the Macbook. Now I need to figure out how to configure Parallels in order for the softphone to connect to the VoIP server. Usually if you can connect to the internet it will be able to connect to the Shoretel server but for some reason it gives me the error that the network card is not working or something. Does anyone know how to configure it for a VoIP softphone?