As far as I know, you need the X11 environment to run that applications tunneled over SSH since those applications require the use of X11. This means you'll have to launch your SSH session from the xterm that comes with X11 in Mac OS X. I've done this from my iMac G5 using Apple's X11. Once X11 launched, xterm would pop up and then I would SSH into my Slackware box (provided that it was configured to forward X11 requests). From there, I would be able to launch applications from the command line such as Gaim, Firefox, etc. But it did require me to do this from an X11 environment.