you can delete DivX player by searching for "DivX" in Finder's search with "System Files - Included" added and delete the DivX Player appication and its support files/folders from the Library.
QuickTime is a layer in OS X which would be VERY hard to remove and i would advise against it as everything that uses it iTunes, Quick Look etc. would crash. but you can delete the QuickTime Player application if you want which is just an interface to QuickTime. QuickTime Player would then be removed from the open with menu.