Then something is definitely
Have him update his sound drivers, as that is always the safe first step. Have him check to make sure he has the headset plugged into the correct jacks, too.
While I haven't heard of this particular problem, it could be the headset. Could he swap it out with a different one, or just use the mic and his regular speakers to see if that's the problem?
If it is his sound chip (Realtek is normally an onboard chip), he could look into getting a dirt cheap sound card.