I found this article is very useful to Extends Out Of Box(OOB ) commerce server 2009 extensibility kit. It will take less then 10 minutes time to extend.
Full credit and Thanks to matin.larijani
Note: Creation of our own namespaces is not cover in this article.
Here you go.
If you have worked with a Commerce Server 2009 SharePoint site (Default Site aka Template Pack) you have probably noticed that the quickest and most efficient way of re-skinning this site is to create new XSLT templates for XSLT Web Parts and manipulating the style sheets (CSS) using SharePoint Designer. Using these tools will give you the ability to leverage the Content Management capability of Microsoft Office SharePoint Server 2007 to manage changes in your SharePoint site