Hi AeroBar
7200 rpm is only important for your "capture" drive that your video editing program saves the video to. The drive (and its interface) has to be fast enough to keep up with the cameras output.
Nearly any modern hard drive is fast enough to capture if the Interface is fast enough. An internal IDE or SATA drive shouldn't have any trouble keeping up, nor should a Firewire 800 external. Even a Firewire 400 external drive is usually fast enough. eSATA is fast enough too but you probably won't find that on a Mac.
The big party pooper is USB. USB does not play nice with moving big files around. It will work but painfully slowly. Trying to use a USB drive as a capture device for HD video probably isn't such a great idea.
A USB drive CAN be used as an external storage or backup drive. It will take a lot longer to move large files around than even FW400, but if all you want to do is move files from one drive to another USB can do that.
But wait, you say.... USB 2.0 is rated at 480Mbits/S and FW400 is rated at 400Mbits/S .... shouldn't it be faster? It's not. Especially when dealing with large files like video files, USB 2.0 can be up to 70% slower than FW400 in read and up to 48% slower in write. I'd call that "480" rating FALSE ADVERTISING.
What kind of system are you using?
Assuming you're using an Intel Mac with a FW800 port, you're best off with a FW800 external drive. Lots of them out there from the cheapie WD MyBook Studio up through LaCie, Iomega, OWC, G-Tech...
Any Mac with a FW400 port, use that.
If you're using an MacBook Air or the new non-FireWire MacBooks, well then you're stuck with USB. I would suggest capture to the internal drive then transfer the files to a larger external drive after the capture in that case.
Good luck with your project,
Have Fun!
Keri