Headset echo

On voice-over servers like ventrilo, teamspeak, mowhawk, etc., whatever I hear on my headset, is echoed back onto whoever else is on the server/channel. For example, if someone were to yell "HEY!", I would hear the "HEY!", and then whoever yelled "HEY!" would hear that "HEY!" as echo on my headset.

The echo isn't caused by my volume, because the echo is the exact volume as what I hear (a good example on that would be music). I'm thinking this is because of my audio settings on input or output, at least that's what I got from google searches. This problem has been going on since I first used a microphone on this computer.

I'm on windows XP using a Realtek sound manager.