In both OSes, the language is installed by default, but IDLE isn't. To get it on the Mac, grab the Mac package at http://www.python.org/download/releases/2.6.4/ , which does include IDLE (it's also a more up-to-date version of Python than the one that comes with the system). After installing, IDLE should be in a Python folder in /Applications.
On Ubuntu, again, IDLE isn't installed, but it is in the repositories; from the command line, sudo apt-get install idle, or use Add/Remove Software, whichever you normally use to install stuff. (I'm almost sure the same thing is true for any of the big/well-supported Linux distros, but I don't know their software repositories well enough to be sure.)
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In both OSes, the language is installed by default, but IDLE isn't. To get it on the Mac, grab the Mac package at http://www.python.org/download/releases/2.6.4/ , which does include IDLE (it's also a more up-to-date version of Python than the one that comes with the system). After installing, IDLE should be in a Python folder in /Applications.
On Ubuntu, again, IDLE isn't installed, but it is in the repositories; from the command line, sudo apt-get install idle, or use Add/Remove Software, whichever you normally use to install stuff. (I'm almost sure the same thing is true for any of the big/well-supported Linux distros, but I don't know their software repositories well enough to be sure.)