Actually what I found worked for me first try was to use wget from the terminal to download the file. e.g:

To get the virtualbox file for windows 8:

  $ wget http://virtualization.modern.ie/vhd/IEKitV1_Final/VirtualBox/OSX/IE10_Win8.zip

As a bonus, you can then unzip it without the zip issues other mac users are reporting

  $ unzip IE10_Win8.zip