webcam partial failure?

Logitech QuickCam Pro 5000; Windows XP Home

[Working on my mom's computer again...] When I run a test of the webcam, the audio and video both work fine (the computer detects my voice and captures the video of me sitting here). When I try to use the webcam while instant messaging, though, I can only receive video and sound - nothing goes through from my end. Friends can't hear/see me, and the video display of myself doesn't even show up on my IM screen.
I have the exact same webcam at home, and it works fine.
No problem capturing a still image with the webcam.
I've tried uninstalling and reinstalling software x3 - nothing's changed.

I'd really like to be able to get this webcam up and running for my mom - she has a hard time writing in English, and I can't read IMs in Japanese. Webcam would be ideal because then we could chat instead of type.

Any suggestions?
Thanks!

 

Finally found something of use at Logitech.com (http://forums.logitech.com/logitech/board/message?board.id=video_clients&message.id=2611) and it seems that this is a networking issue, not a glitch with the webcam itself. Something to do with all my mother's ports being "stealthed" or something.
I still don't have a clue how to remedy the situation, and I'm not going to be at this computer again for another couple of weeks - but if anyone is in the position to offer any ideas, they would be most welcome, and I'll get back to troubleshooting toward the end of the month!
Thanks!