Flash MX is the name of the authoring program for Flash Player 6. It is two versions behind, but a majority of the actionscript language and almost all of the design view is still very similar in the newest version.
It is somewhat different, MX is a previous version of Flash. There was Flash MX and MX Professional, then MX 2004 and MX 2004 Professional, then Flash 8 and Flash 8 Professional. most of the same concepts will still apply, you just won't have some of the features of the later versions.