possible to share game between Windows and linux?

Hi,

If a person has one windows and one linux computer but in different places, is it possible to set things up with CIV IV Complete so that they can start a game on the Windows machine and then continue it on the Linux machine ?

Using Dropbox folders ? USB-keys ? Steam version of the game ?

Or is it a waste of time just trying...?
It for a potential gift so I cannot try it out myself before asking.

Thanks!