Yes, it is. I've just introduced NASA World Wind to over 2000 teachers in the last month or so. Very awesome. Takes a good computer with a good graphics card and fast internet connection. If you want to see the actual download site - http://learn.arc.nasa.gov - you can get other cool programs the Learning Technologies Project has done - and they're free, too.
http://www.download.com/World-Wind/3000-2054_4-10374180.html?tag=lst-0-3