Either VNC to it (OS X's built-in "Screen Sharing" does VNC,) or use remote X via OS X's built-in X11.
Just search for X11.app, load a terminal from there, and launch a standard remote X session. I do that to run apps on my Itanium box from my Linux-running Netbook. It's funny running the gnome-system-monitor on a netbook and seeing 16 CPUs and 32 GB RAM.