No sound from mic in video call

When I run a video call, I can see the other person's web cam and hear them,
but they cannot hear me. My settings show up as fine and my mic and cam work
in Skype with no problems. I've tried to find a solution for this but most of
them seem to be connected with Vista. I run XP Professional x64.

Bit of an update, we have both tried disabling our firewalls to see if that
affected it at all, because I've read that that was a possible solution for
such issues with XP. No such luck.