To answer some of your questions, I was able to connect by plugging the
Vonage adapter directly into the cable modem.  I already have a separate set
of queues set up for Vonage, and I only switched to Vonage after I got cable
Internet.  I'm fairly sure that if I can dedicate bandwidth to vonage rather
than prioritise it that this will clear up.  I'll also try to post my config
files again (30 KB limit again).

Thanks for your help,

Richard