There's not an appliance per se but you can just install it to a virtual machine. I was running a 1 CPU, 256MB instance with a 100mbs line and noticed no issues - ESX running on Core i7-920
I really thought they had a blog post somewhere or maybe a tweet or something stating they were planning to support a vm, but I'm failing to find the link. Maybe I'm remembering incorrectly. In any case, they do have a forum section dedicated to virtualization:
