Ok, Ventrilo is not working for me, when i see the screen of CS:S it doesn't work, but when I alt+tab it works, I want to know why it wont work while i'm in side the game playing.
What I would do is first restart your computer (if you haven't done so already [in my experiences, 90% of computer problems can be solved by restarting the machine]). If restarting doesn't fix it, try uninstalling and reinstalling Ventrilo.