We've run video over several types of vpn. The one setup we are currently using while waiting for lines is a Polycom FX H.323 on a 10/100 switched network, connecting through a PIX-515 (56bit) and a 512K connection to an VPN-3030 on a 6Mbps DS-3, then connecting to another FX. The quality varies dramatically on this setup. Sometimes the quality is as good as I get on my MPLS WAN, sometimes the systems won't even connect. This is an international link, with quite a few hops and occasionally latency problems. We've also used a similar setup with an FX going through a pix/t1 to another pix/tl, which worked fairly well. We originally had two different isp's, and after switching both offices to the same ISP, we noticed significant improvements in video and audio quality. As you can imagine, the overall improvement from being on one backbone helped immensely. The biggest suggestions that I can make are to use the same isp at all your locations, get the biggest pipe you can afford, and time your important calls at times when other network traffic is low (monday mornings are usually good to avoid).
Good luck, and if you further question, don't hesitate to post them.
Andras
