iChat and broadband speed

My inlaws and I are trying to figure out why they get such poor iChat performance. We videoconference with them often through iChat, and their sound cuts out, or the picture becomes so pixilated that they can’t see what is going on.

I just ran a Speakeasy speed test and it doesn’t seem that our connection speed is a problem—our speed to their servers in New York (very close to my inlaws) is pretty darned good:

18065 down 1960 up

So that leaves a few other possibilities. One is my inlaws’ speed—I know a few other people in their neighborhood have gotten cable modems. Another is iChat version—they are still on Mac OS X 10.3 and we have made the Tiger move.