Did you manage to fix this Check 6?
I just installed a webcam on my PC (win 2K, sp4) - both my Dad (win xp. sp1) and my brother-in-law (win xp. sp1) bought the same camera too.
Using MSN messenger we can send a webcam image to each other but we can't get audio to work - it keeps on saying that it is connecting but nothing happens thereafter. Basically same problem as yours.
I've searched Google high and low but can't find a definite answer.