I think the problem with USB is that it may have the capability to do 400 Mbit/s, but it only does so sporadically. USB won't do 400 Mbit/s sustained, whereas Firewire will push high bitrates consistently and constantly.
I guess I can transfer files from the external to the internal when I want to view them, but that sort of defeats the whole purpose behind streaming anyways. My desktop only has a 160GB and my external is 500, so I guess I'll have to get a bigger internal if I want to stream. I guess I will just have to stick with carrying the external back and forth. Lame.