Friends cannot see me on MS LifeCam Cinema webcam

I purchased Microsoft LifeCam Cinema which appears to have installed
correctly. However, when I start a video call in WLM, I can see both myself
and my friends, but they cannot see me. Does anybody know what the problem
might be?

Is it necessary to rerun the setup program every time I start WLM via Tools
| Audio Video setup, or was running it once sufficient?

If I start WLM, but without initiating any video calls and then check the
Processes list in Task Manager, MSCamS32.exe is running. Should that be the
case?

Do any ports need to be opened in the firewall to allow my friends to see
me? I'm running a third party firewall, namely Comodo Internet Security.

My OS is Win XP Pro SP3 with all the latest patches installed.

Thanks in advance.