Bad news saint, I figured out a great way to do this... and cheap!
So with that program all you need is a xbox 360 mic (I have mine from rockband).. it's usb based so it's a not a problem connecting it. Windows does the mixing.
you don't need to setup anything in win 7 (it automatically downloads the mic driver when you connect the mic), in win xp you may have to just find the driver and install it yourself. If you have a usb plug somewhere on your setup you can easily connect it and put it away when it's not needed. Same thing with the xbox 360 rock band guitar, I'm using it with guitar hero world tour on pc (I imagine it would work just as well on frets on fire).
You can find the rockband mic on ebay for about 15 to 20... I just saw one for 15 + free shipping.