One of the frequent question that I get is how to customize the top navigation of SharePoint page to look the same as Enterprise Portal navigation.

http://msdn2.microsoft.com/en-us/library/ms476046.aspx details how to customize master pages in SharePoint and apply it to all sites.

Not all the pages uses the default.master as the master page. The pages that are served by _layouts use application.master. So this also needs to be modified to provide consistent look-n-feel and top chrome for all the pages.
http://msdn2.microsoft.com/en-us/library/ms476046.aspx talks about master pages used by _layouts.