jEdit should work fine with the later commercial versions of Topas. If you've installed within the last year or so it should get set up automatically. The "->TA" button works with either version. To launch the commercial version use the "red jewel" icon rather than the "TA".
If you installed jEdit a while ago you can update the menus from:
http://www.dur.ac.uk/john.evans/topas_academic/jedit_update.htm
If that doesn't work you can always bypass the "->TA" button by using "Launch/Set Input File" in the topas menus.