In recent versions of Mac OS (at least since 10.5), you can type the accented letters of Esperanto very easily, without downloading anything or using a website, as long as the language of your system is English.
To prepare your computer (required only once):
1. Open “System Preferences…” from the Apple menu.
2. Click on “Language & Text”, or “International” (depending on your version of OS X).
3. Click the tab “Input Sources”, or “Input menu”. You will see a long list of languages (keyboard layouts, in fact). If you live in Australia, chances are “Australian” is already selected.
4. Scroll down to “U.S. Extended” and select it. (NOTE: Depending on your version of Mac OS, this is probably “ABC Extended” now.)
5. Scroll up again and deselect “Australian” (or whichever keyboard layout was selected before)*.
6. Close the window.
Then, to type the accented letters, do the following:
For ĉ, ĝ, ĥ, ĵ or ŝ, press option-6, and then c, g, h, j or s. (This also works for the capital letters.)
For ŭ: press option-B, and then u. (This also works for Ŭ.)
(The reason for “option-6” is not surprising, because above “6” on the keyboard is “^”. “B” is obviously from the word “breve”, which is what the ˘ symbol is called.)