Hi Rochai and welcome to the RH forums.
When you create a new RH project you'll notice options near the bottom of the wizard to import existing content. You don't say what format you were generating from AuthorIt. Try this import option and come back to us with some more details if this doesn't meet your needs.
Try exporting from AuthotIT in XML and importing the xml into RoboHelp.
Let us know if that is sucessful.
Sorry Peter I don't have AuthorIt available at the moment only Robohelp.
However I did work with AuthorIT for a number of years and you can defintely export XML.
This link on the AuthorIT site gives a description of the objects included in the XML and looks like TOC and Index are included.