Problems with VOIP - Help needed

Hi all, been having problems with my computer.
I play many different games, most of them online. my favourites are BF2, BF2142 and GRAW.

When I play these games, I usually use some background 3rd party VOIP software to chat to my friends at the same time, like teamspeak or ventrillo.

Problem comes when I have been playing, after a littlewhile, there will be some sound problem, I'm not sure if its a hardware fault or a software fault.

I will stop hearing what the other people in the VOIP software are saying to me. If I ALT+TAB back to windows The software still registers they are still speaking, but there just isn't anything coming out of the speakers. At the same point, I usually loose some of the ingame sound.

The problem can always be rectified by exiting the game and restarting it. Exiting and reloading the VOIP software has no effect.

Anyone else have this problem??

It happens on lots of different games, so I'm thinking its not down to the games.
I'm running on AMD X2 4200+, 2GB OCZ Platinum RAM, Asus A8N 32 SLI Deluxe, Creative X-FI.

I'm not sure which forum this is most appropriate in as I'm not sure where the fault lies.

Any help most appreciated.
Cheers
CC