Nope. While on Windows, Linux, and OS X you can have two remote users logged in and independently using tty windows, they all must share the same GUI window.
X (the service commonly providing the *nix GUI) was pretty much built with this in mind; Linux has had an implementation of X that has provided this since at least the mid-90s.
Windows has had this on the server since at least Windows Server 2003, and has also introduced it to the "consumer" market in Windows 7.
(I'd be happy to find out whether OS X supports this or not.)
I have Windows XP, and have had 2000, NT, 98, 95, etc., and none of them could do it.
I'm glad to see that finally this "40 year old technology" is getting onto desktops in the last year or so.
The first way is by remotely running a program on your own Xserver. The programs' processes occur on the remote connection and are sent down the SSH tunnel and show up on your display. This is the common way in Linux.
The second way is by an older program from the Windows world: VNC. VNC takes a local, running display (example: my gui) and allows someone else to view/control it at the same time I do. In this method, you both fight over the mouse and keyboard inputs.
http://www.apple.com/macosx/whats-new/features.html#screensh...
My older Mac Mini would not do it. I didn't know that this was added in 10.7.