asterisk users - Apr 2003 - just static on netmeeting call to extension

Hi Folks,

Trying to make h323 work with asterisk, I got netmeeting to call an extension. 
The extension rings and, as I answer the call, I can hear my voice echo on my 
headset, but I cannot hear my voice on the phone - just static (the static 
increases when I speak)

any hints?

Thanks!

PHM