if i get a network hard drive will i be able to access it from anywhere?

im looking to get a network hard drive [particularly the lacie Ethernet disk mini 500gb] and i would like to set it up with ftp so i can access my files from anywhere with an internet connect. i dont know too much about networking, so im not sure if i will only be able to access it while im connected to my home network. i am on a macbook pro but want it accessible for windows user also.