The Product Name field is a tool that you can only add to the opportunity detail view and that lists the product names (with or without quantities) of the current opportunity. The purpose of the tool is not to display in your layout information you already have access to under the Products tab, although you might find it convenient.
The idea is to have this information written to a field of your choice, ie. the field you associate to the tool when you insert it in the layout, so that you can display that field in the opportunity list view and consequently so that you can see the product names in the opp list view, a feature that is not available in ACT! 2010 anymore.