Vista - jumpy sound and video and sound

Hey Group,

My oldest son, oldest daughter and I just installed Windows
Live Messenger on our machines.Without going into a lot of
details about each of our machines, suffice to say, each of us
has everything power wise to handle the program. My Son
is on cable, I have DSL as does my daughter, also of sufficient
bandwidth to handle the program.

My daughter and I were the first to communicate with the program
and it went beautifully. She in West Virginia and I in Oklahoma.
When either of us contact my Son, also here in Oklahoma, his
sound and video is so jumpy, jerky and distorted that we cannot
understand him. The video is better than the sound but not much.
My son and I have literally the same Gateway machines. As I
said I have DSL (1.5) and he has Cox cable broadband.

I know there is some simple little quirk that we are missing that
will bring him up to Parr, but it has completely eluded us until now.
Please offer suggestions on what we might be missing with this
program to make it work correctly.