how to run a database off an external harddrive?

i've got mysql 5.0 and I have 50 million records in a text file on an
external USB 2.0 hard drive. I can import the file into a mySQL
database on my laptop - but I don't want the database on my laptop. I
want that database to be physically located on that usb connected hard
drive instead of my laptop. Can anyone tell me how to set up the
database on my laptop, but with a physical location of the data on the
external hard drive? Oh - not that it helps, but I'm using Navicat (my
first day using it).

Thanks!
jason shohet