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I wouldn't recommend trying to set up the OS on one. The available bandwidth is lower than the marketing numbers suggest.
USB 2.0 is 480Mb/s, which is the equivalent of 60MB/s. Overhead for the protocol will reduce that to about 50MB/s. Latency will be much higher than on an IDE interface as well.
Firewire, last I checked, is 400Mb/s, equivalent to 50MB/s. Overhead is less than USB, but still takes a toll. Again, latency will be high.
Either will probably run an OS, but not quickly. Additionally, you will need the controller drivers on FDD to load the system. That's quite likely to be an adventure and may require you to create the txtsetup.oem file and configuration. The drive will likely only be bootable on the system it's loaded from, unless the hardware is identical. Even then, you may have activation issues if you are planning on using XP and changing between systems, as this is technically a violation of the COA and you'd really need a liscense for each system.