I don't believe the 5big has any utilities to allow remote access.
Therefore you'll have to set something up from the mac side of things to share the drive.
What is the intended use? If you just need access to files on occassion, I would try
http://www.logmein.com and setup a remote login, but that is sharing your whole computer basically.
If you actually need to "share" files on the device without screen sharing, then that's beyond my experience level (although it's easy to do with mobileme from what I read), maybe someone else can chime in.