[Will Salley] "I've downloaded several different files"
There's only one file that's appropriate (well two, English or German) and being only 100 MB it shouldn't take 20 hrs, unless you are on dial up, I guess. but as long as you went to Downloads/Documentation ( this page -
http://www.maxon.net/pages/download/documentation_e.html ) and clicked on the + sign next to this - CINEMA 4D Release 10.111 & BodyPaint 3D R3.111 - one of those two files should be the right one (the english I'm assuming). Unless you have a corrupted install or something (unusual). Unless someone else here knows something more, you might want to email support.