You know that command-shift-3 works is System 6 too, right?
LOL! I love that that command key combo had gone unchanged since 1984.
Depending on what you are doing Mini vMac may be a much better option for you. That's where I get all of my screen shots. Now that the developer implemented a script to import and export files to and from the real Mac it's a piece of cake! Not to mention window screen shots have always been available under OS X with (command)⌘-Shift-4, then press the Space bar. Move the pointer over the area you want so that it's highlighted, then click.