217562 Joomla Multiple Site Fix

Hi, I don't feel like bothering with a component at this point. I duplicated a new site I am working on and need the user information synced. Site one is the main site, and site two is located on a sub-domain of the same site. Site 2 will contain the user log in and forum, so I need the information input into site 2 to be automatically updated in site one. Please let me know about the changes made so that I can manually do them myself/fix them if needed again. Thanks.