in vent setup, set the input device to enable 'use directsound then set the name to the creative headset.
set the outbound amplifier to 0
what's your upload bandwidth?
www.speedtest.net
what is the codec/format the server is using? rt-clik in window/view/server browser
also checkout this thread:
http://forum.ventrilo.com/showthread.php?t=45745