Hi,
You can specify which styles are displayed in the Styles pane. By default, Word displays "Recommended" styles, but if you click on the Options... link at the bottom of the pane and choose "In use" instead, you should see your custom style (but you may
lose others that you haven't yet used but might
want to).
You can be even more selective by clicking on the Manage Styles button (it's the third icon from the left at the bottom). On the Recommend tab of the Style Manager, you can assign priorities to the style and make them visible or not (or "Hide until used").
You can get a lot of very fine-grained control this way--probably more than most users really want to bother with!
You can also right-click any style in the Styles pane and either add it to or remove it from the Quick Styles gallery.
Hope that helps.