Shoutbox

I have MSN mes 7.0 and plus, I use a logitech quickcam with built-in micro and my contacts, when using video-conference don't hear me, they can here the sounds from my computer, like the music I'm hearing and stuff like that, but not the exterior sound.... I've tested the webcam and the sound it's great.... I can even listen to my breath....
does anybody know how to solve this..........