How can I speak while on CF?

I use Ventrilo to talk with my clan while I'm on CF during cwars etc.
However, when I play CF and talk on vent, no-one can hear me but my clan mates can talk perfectly and I can hear them. If there any configuration I need to do to be able to talk while in game in crossfire? I tried asking my clan but apparently, it already worked when they first installed ventrilo. So, how can I make it work in game?