Could you confirm in what site you are adding the web part? Is it a publishing one. Also confirm if there is an approval functionality enabled in your site? In general RadEditor for MOSS uses impersonation as user rights management so the answer of your question "Is there any function that I need to activate?
" is that there is no RadEditor for MOSS one. However you need to setup SharePoint's security and user settings so the other user will be able to view your changes.