Hey scottstevens,
I'm not sure about your CPU load question, but and interesting tidbit for you...if you're looking for something really portable, the have <A HREF="http://www.coolerexpress.com/usb20coex25i.html" target="_new">laptop harddrive(external)</A> that are much smaller (2.5"), about the size of a pda...they can also be powered off a laptop's USB bus, so you don't need to plug them into a wall socket. Firewire does not have this capability.
BTW, what program did you use to rip to MPG4 format, I was looking at Dr. DivX and tried the demo, seems to work pretty good, but I was wondering if there are better ones out there? It was $50 for a Dr. DivX license.