Several options control style visibility.
First, click on the Options button at the bottom of the Styles Pane (2007). Make sure "In this document" is showing. If that doesn't solve it, go to the Styles Manager (third icon next to the Options link), find the style in the Recommend and Restrict tab lists, and Show and Permit, respectively, the style you want.

If you don't find the style, copy a word in that style from a document or template in which the style is available, to the document in which you wish to have it. It will bring the style with it. Unless one of Word's other bells and whistles is checked wrong...

Best,
Ulodesk