Firewire is the way to go with your project. Although the theoretical speed of USB 2.0 is faster than Firewire 400, it has so much overhead and is so processor intensive, that is seldom achieves that speed. Firewire, on the other hand, is capable of sustained transfer rates at close to its limit.
Besides that, Firewire works better on a Mac. Had you asked the same question about a PC, I would have mentioned FIrewire and pointed you toward USB 2.0. For some reason, it is better on a PC. That said:
You should be able to daisy chain the FirePod and the Hard Drive together without a problem. You may want to consider a Firewire Hub (Powered) to give yourself a little more flexibility. Instead of purchasing a ready built Firewire Hard Drive, consider purchasing a Firewire enclosure, one capable of exceeding 127GB, and purchase an IDE drive for it. IDE drives come with huge capacities, 400Gb are off the shelf items, and are relatively cheap. 400Gb@7200 = $400 this morning at BestBuy. You can almost certainly get them for less than that. Installing the drive inside the enclosure is a no brainer.
Hope this helps. Will you be using Garage Band?
P
I'm not too familiar with the peculiarities of the FireWire interface, so I'm hoping for a little enlightenment. My band is looking into getting a nifty FireWire interface, however each of the two Apple notebooks that we could use seem to have hard drives that are a bit too slow. So it occurred to me that if we wanted to do this with a notebook, we would need an external hard drive. Now, I would be open to suggestions on either USB 2.0 or FireWire 400 hard drives, but my question is, if we get a FireWire one, would we be able to daisy chain the recording interface and the hard drive together, and get them to work with the system? Let's assume that the interface is a PreSonus FIREPOD 10, and the operating system is Mac OS 10.4.2, in case that would change anyone's bearings on the issue. Also, would any of the USB hard drives out there be adequate for a home recording studio (fast enough, large enough)? Any of the hard drives suggested would have to spin at least 7200rpm.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic