Vista - VoIP poor sound

Hi there.
I have a small (?) problem with 2 programs I use to make calls, VoIP Cheap
and VoIP Discount.
Both install right in Vista RC2 5744,but when I try to make a call with any
of the 2, I got a cracky and broken return sound, and my transmission are
broken and unreadable (that's what they say).
Is there any codec missing, or any secret setting within Vista?
For info, Skype works fine, both audio and video, and the sound I get from
WMP or Winamp is very good.
One more thing, it does not matter what kind of mic I use, the built-in (my
PC is a laptop), a mic attached to the mic port, or a USB headset, or the
Logitech camera built-in mic.
Thanks
José