Slow hard drive to hard drive transfer for mpeg files

I just hooked up a new Simpletech usb 2.0 drive. I'm having an odd
problem. If I try to copy or move, for example, a 2 gigabyte mpeg file
from my internal IDE hard drive to the external drive, it takes
forever. The progress box showing the copy or move estimates it will
take over an hour. However, if I try to copy or move the equivalent
size (2 gigabytes) of non-mpeg files--pdf, word, jpeg, etc.--the
transfer takes place in less than a minute. I have another computer
with usb 2.0 drive that does not have this issue.

Anybody have any idea what might be going on? Is there a problem with
the Simpletech, possibly? I don't see why the copy/move is so different
in terms of time depending on the type of file.

Thanks.