If I understand correctly, you want to tweak and customize the Alfresco Explorer's "Getting Started" dashlet.
Note: Please follow the customization guidelines, by moving to extension directories, though I have not mentioned anything about it below.
1) You will have to start editing from <ALF_HOME>/tomcat/webapps/alfresco/WEB-INF/classes/alfresco/web-client-config.xml to add your new dashlet.
2) Write webscripts desc, js, jsp (<ALF_HOME>\tomcat\webapps\alfresco\jsp\dashboards\dashlets) for your new custom code and add to the code base - using (replicating) the existing Getting Started code.
3) Once you have registered the new webscript, I think you can add the new dashlet via the user interface.
Let me know how it goes! Hope this is helpful!