I don't think you are able to copy the entire page, but it is possible to copy the modules to a page on a sub-site. Though, it's not possible out of the box. You would need to add functionality to be able to do this. 

Here are some links that may be helpful:

• http://www.dnnsoftware.com/forums/threadid/458914/scope/posts/dotnetnuke-sso-single-sign-on-and-site-groups-in-ce
• http://www.unisols.net/DNN-TIPS/articleId/2/articlesListTabId/57/articlesListModId/431/articleDetailsModId/431/listType/templateBased
• https://dnnportalgroups.codeplex.com/

I would test these out on a testing instance of DNN before putting into production.

Since I am new to DNN, please tell me where is the DNN file system to put the file into