Thanks for the reply. Yes, it actually is a new switch (new to us, we got it from another lab). It's a cisco 6500 type thing. We actually just got frisbee to work by explicitly disabling igmp snooping. My understanding is that this makes multicast traffic behave like broadcasts. But at least it works!
But you could overload your switch pretty easily. There are detailed instructions on our Wiki about configuring your switches. Lbs