You have to do what's called "mounting the drive." The external drive must look like a regular drive to the linux machine, and this is accomplished by mounting the drive. Think of it as a transparent shortcut to the external drive, where for all intensive purposes, the linux machine treats the drive as if it is attached directly to the machine. At that point, the path to the external drive would look like the path to any other internal file or folder.
To learn more about mounting a drive, do a google search for "mounting linux smb."
Also, this thread may be of interest to you as well:
viewtopic.php?f=2&t=8590&p=35397