Not difficult at all to do the split with Gmaptool, a thread of Gmaptool can be found here [Only registered and activated users can see links. ].
Tip: the Sticky threads are really good and well organized, start there when having a question

In short, load the .img file with Files, go to Split and fill in the paths and preferred names and do the split.
Run the install.bat file, as administratror in Win 7 and the map will show up when starting Mapsource or Basecamp.