Hello,
You could use Teamspeak http://teamspeak.com/?page=teamspeak3
Roger Wilco http://download.cnet...50_4-48440.html
or Windows Messenger for voice when flying. They are all free.
If you headset is usb you will be able to select it separately and the sim sound will still come from the speakers.
If your mic and headphones plugs into the sound card you will probably need two cards to keep them separate.
Bill