Running Avast 4.8 Professional with pre-release Beta thing installed. I can play World of Warcraft without any lag, but when i run Ventrilo in the background while playing, all lag returns and it's even worse than before applying beta patch. When i press Push-To-Talk key, it actually stays pushed for 5 minutes or so, lag is that bad. This leads me to conclusion that lag might actually be caused by some other conflict than WoW vs Avast? I tried also with Self-defence mode switched off, but lag persisted. When i quit Ventrilo, i can play WoW without problems again. Haven't tested Teamspeak's behaviour yet. So far, i'm forced to uninstall Avast before raid so i can play smoothly, and then install it back after we finish. It's getting quite annoying but have to cope with it for now as we have to use Ventrilo.
CPU - Intel Pentium 4 3.4GHz
GPU - nVidia GF 7600GT
(so AMD/ATI chipsets do not seem to be the cause of lag either)