It is possible to buy a 2TB drive, make it into gobs of partitions, and install a different supported OS for that particular machine on every single partition. One install does not affect the other partitions. You could have five different installs of Tiger, five of Leopard, etc. There is not a good reason to do this, but you could. You might be violating the software license but maybe not, I'VE NEVER READ IT! (Even the lawyers who write it have never read it.)
You could also run boot camp and have one partition for Windows, several for Mac, and several for Linux. It really is up to you.