XP Pro Phone Dialer Problem

I have plugged in a headset w/mic into my sound card. When I try to make a phone call, it connects, and the person on the other end can hear me fine. But I can't hear them when they speak. The headset works fine when listening to music or the radio, just not when trying to conduct a phone call. I have went into the phone dialer settings and have changed the speaker properties to stereo headphones. I can't seem to think of any other options, any ideas?

 

Yes, the headset has 2 jacks and they are both plugged in to the sound card. I have checked all volume controls, The sound card has been selected as the source for the headset. It has to be a software problem ( I assume ), but I can't think of where else to check.