Every Macintosh running System 6.07 or higher can support Text to Speech, which uses a computer synthesised voice to read text to you.
The name of the technology keeps being changed as new versions are released, in MacOS 8 and higher it's known as Text to Speech, and it's part of the Speech control panel, and uses the Speech Manager extension, but if you have an older system version it might be known as PlainTalk or MacinTalk. In some versions of the MacOS you have to customise the installation for Text to Speech to be included.
Text to Speech may sound like it's just a toy, but it's actually a really good way to grammar check your document. By having the computer read your text out to you you will notice errors more easily than by reading it.
Many Word Processors have Text to Speech support built in. There are notable exceptions to this, such as AppleWorks. If your application doesn't have options for making the computer read your document, copy and paste the text into SimpleText.

The Sound menu in SimpleText lets you choose which voice you want to use. Not all of the voices are particularly good, I've found that Agnes, High Quality or Bruce, High Quality are generally good for proofreading. The Speak All menu option changes to Speak Selection if a portion of the text is highlighted, which means that you don't have to listen to the whole of your 10,000 word article if you only want to hear the last two paragraphs. You can stop the speech at any time either using the menu, or the universal stop shortcut, [command]-period.
Apple Speech Technologies Website
PlainTalk - MacOS 6.07 to 7.6.1
Newer versions of the software are included on the MacOS Installation CD/floppies.
