RSLinx Enterprise is what the new communication engine/drive for the FactoryTalk enabled software. RSViewSE (FactoryTalk View SE or something like that now), RSView ME, RSSQL, etc. RSLinx Enterprise uses the FactoryTalk libraries for the RT tag database (forget the markeing speak for what Rockwell calls that part).
It is also what is used on the PV+, RSView ME Runtime and the CE boxes with RSViewME runtime. RSLinx Classic is used for the older software like the different versions of RSLogix, RSView32, etc.
Darren