msn Messenger voice problem

I can not get the voice in MSN messenger 6.1 to work on
this pc. I have two other pcs that it works fine on. This
one has winXP Pro, the others have Win2000. It has an
Audigy 2 ZS sound card with speaker and Mic connections
in the front and rear. I use the front connections for
Word dictation, and they work fine. I cannot get the
Messenger tuning wizard to recognize the mic in the front
connection. It sees it in the rear connection and sets up
OK, but I can not send out any voice from it. When I try
to send a voice message to a contact,the volume bar moves
as it should, but no voice goes out. Same problem with
the phone thru messenger with net2phone. This pc and one
other are hard wire connected to a router, the third pc
is connected to the same router wirelessly. The other
two, one wired and the other wireless, communicate fine.
I can receive voice on this one, but cannot send out
voice. I have the same problem if I try dial-up. Any
suggestions will be greatly appreciated; I have tried
everything I can think of. Thank You.