Consider only USB 2 or Firewire. A firewire card is about US$30 and a Firewire housing with Oxford 911 chip is around US$120.
A USB 1.1 hard drive would be like pulling teeth. It's so painfully slow.
Think about it.
ATA33 drive: 33 MB/s. There are drives that are faster than ATA33 now.
Firewire drive: 35 MB/s
USB 2 drive: comparable to above
USB 1.1 drive: 1.5 MB/s
EDIT:
<<
Here is a link to a USB hard drive review. Below is an excerpt from page 2 of the review. >>
Eek! That USB drive
couldn't even hit 0.7 MB/s peak! That's barely faster than even the ultra slow USB zip drive. In contrast, the IBM ATA100 drive hit 42.4 MB/s, with an average read speed of 32+ MB/s. Why Firewire (or USB 2) is good: From reviews, several Firewire drives have been shown to go over 30 MB/s.