mod rewrite and duplicate content

[mntoner]

Suppose you have a page in your site: http://mydomain.com/index.html which has information about cheap widgets. Further suppose you use a mod rewrite and create a url http://mydomain.com/offers-cheap-widgets/ which points to the same page. The purpose of this strategy is search engine optimisation of the widgets page (keywords in the url etc).

Would this lead to duplicate content in the eyes of search engines? And what result would this have on your serps?