I quickly "tested" EV Nova (two more finals, dang it), and everything worked fine. It was a copy off of my iDisk, although it possible that yours was somehow corrupted. To quickly check if it did, open up the Terminal, type openssl md5 and a space, and then drag the EV Nova.dmg file onto the terminal window, and type return. Your command should be something like
adcockb% openssl md5 /Volumes/Icarus/Downloads/EV\ Nova.dmg
and the returned response should be exactly
MD5(/Volumes/Icarus/Downloads/EV Nova.dmg)= 29fe1e8716dd3da5efe72478fa00ffcd
(well, the directory part can be different, but after the =, it should be exactly that.
If it's the same, your download was fine, and it's another problem. If it's different, you'll have to redownload it.