Pages doesn't have this feature. There is an autofill preference but it is limited.
You really need a third party app like
Textpander. This is a great little app that you can copy and paste text into and assign a shortcut. The text will paste into any text document including e-mail and non-cocoa apps like Appleworks.
The only disadvantage I have seen to Textpander is its sluggishness. It is very slow to open for the first time after a restart and there is quite a delay when creating abbreviations. Once you have data in there, however, response is immediate. Type the abbreviation in your text app and the template is quickly pasted in.
Kurt