In either case, you may choose to download the University of Pennsylvania morphology database (if you want to do morphological analysis) and/or the reverse morphology database (if you want to do morphological generation in change rules).
If you choose to download the source files, you will also need to download the Tcl 7.6 and Tk 4.2 libraries. Also, if you intend to change the token grammar and lexical scanning rules, you will need to download the bison/flex plug-in for CodeWarrior.