I have a site using Plone 4.1. When I'm logged in this site, news are displayed with the author and the last modification time. But that information disappears when I visit the site as an anonymous user. ¿How can I configure news to be showed with they creation date and with the creator name? Also I don't want to display the last modification date and I don't wan't to use all decimal digits in that times.
You're referring to the viewlet: plone.belowcontenttitle.documentbyline. This viewlet's behaviour is common for all content types and it's not configurable (like almost all other viewlets). Though, it's quite easy to show this viewlet to anonymous user without any customization:
just go to Zope management interface -> portal_properties -> site_properties and enable the option allowAnonymousViewAbout.
But if you want a different behaviour only for news items, you have to hide that viewlet, create a new customized one that behaves differently depending on the context's content type.
More info: