Best practices for mounting Linux filesystems on OS X over the Internet
First, set up a VPN connection between the VPS and your Mac. Something like OpenVPN is fine (the TunnelBlick Mac client works well, at least up through Snow Leopard).

Second, set up the VPS as an AFP server using the "netatalk" package.  Something like sudo apt-get install netatalk.  AFP is the native Mac network filesystem.  Configure it to your situation.

At this point, you can establish the VPN connection between the VPS and the Mac, and then find and mount the AFP volumes from the VPS in your Finder.

An alternative would be to use something like MacFUSE and SSHFS, but using AFP is more "native" and will show up better in Finder.