I'm a newbie to COGNOS - in ReportNet, is a Package similar to a Catalog?
Packages contain the business information and is the definition of the underlying database(s). If you click on the package explorer you can see the structure. Business info/rules can be included into these packages that cannot normally be included into databases eg. the calculation of profit.
That description sounds very much like an Impromptu catalog to me, at least in functionality.
Yes, a package is equivalent to a catalog.
It has a lot more flexibility, but does not do everything the same way as catalogs (not that that's a bad thing).