Voicing problem

I have been using voicing over ICQ using their ICQPhone PC to PC voicing
facility.
I have used it on several PCs and am pretty familiar with setting it up and
using it.
I am in the initial stages of trying to setup peer to peer networking
between my two PCs both using XP Pro.
What I have setup so far has stopped ICQPhone from working on my main PC.
I have not got as far as tring to access the internet via the local network
using the second PC.
I can connect, but cannot receive or send audio.
A local test of voicing in ICQ fails.
Voicing using MSN Messenger still works fine.
I would like to isolate the cause before proceeding with my networking.
How would I isolate the problem?
What procedure should I use to disable/uninstall my networking changes one
step at a time to try and restore voicing, and ascertain what exactly is
causing the problem?
Or even to restore voicing at all, even if it means abandoning my networking
facility altogether.

Any help would be very much appreciated.
Brian Tozer