External for Video Editing (that the MBP can handle)

I have a 15" Macbook Pro thats about 2 years old.

I recently got the Western Digital Studio Edition 500GB External HD. I mainly use it for creating video's. The idea was to capture video through my MBP directly to the External HD. However the MBP seems to have problems running both the Firewire 800 and Fire 400. I have the External in the 800 and my Camera in the 400. (Both are plugged into outlets also including the MBP)

More often it just disconnects one of them and pretty much wont support both at the same time.

Question: Is this just a crappy part of MBP? (not sure if its been fixed in the updated ones). Or is there other External's that will be able to do what I want and run both firewire's at the same time?

how does it work if you capture to the internal HD?

I can capture to the internal drive but I just dont have enough room. It's far easier to go straight to the external then have to always free up room on the internal. Plus I'm using Final Cut Pro so everytime I would have to reset the files and such.