Unfortunately EclipseCrossword is only available for Windows so you cannot install it directly on OSX on a Macintosh computer without the use of third party software. This leaves you a couple options if you only need to view the .ECW files including installing EclipseCrossword via third party software on the Macintosh or have someone with a Windows computer convert the ECW file to a format you can view more easily on your Mac. Below I describe each option in more detail.
Install EclipseCrossword Using Third Party Software On Mac OSX:
The first option would be to install EclipseCrossword using third party software such as Microsoft Virtual PC For Mac, Apple Bootcamp, or Parallels Desktop. Each of these applications will provide you a method for installing Windows applications on your Macintosh. If you already have one of these applications you can simply install EclipseCrossword through MS Virtual PC For Mac, Bootcamp, or Parallels using the same basic directions described in this article.
Use A Windows PC To Convert Or Export The ECW File:
The other option would be to have someone with a Windows computer export the ECW file to a format that you can easily view. We recently wrote this article that describes exporting an ECW (EclipseCrossword) file to WMF (Windows Metafile) format which can be opened using various application on Windows or a Mac. On Windows WMF files will open by default using MS Paint however they can also be opened using Adobe Illustrator, Adobe PageMaker, ClarisWorks, CorelDRAW, Corel WordPerfect, Deneba Canvas, HiJaak, Microsoft Publisher, Microsoft Word, Microsoft Excel, Microsoft Powerpoint, Microsoft Works, PrintShop, QuarkXpress, and Vueprint. On a Macintosh you can use all of the same applications except for Illustrator but you can also use GraphicConverter that is for the Mac only. If you are having a friend convert the file you might consider having them convert the WMF file to something like a GIF or a JPG which are more universal file formats.
I believe many college professors use EclipseCrossword for their students and then will provide answers in ECW files which is not convenient for students so you may consider asking your professor if he could go ahead and do the file format conversion for you if you are using a Macintosh running OSX.