Not sure quite whats going on with these atm, but I've got them downloaded and installed but not showing up. Some dev recommended creating a blank challenge in the editor to generate a config.xml... but still, no dice.

However, I've since stumbled across a way to get them in. No idea why this worked, but hey.... all the best solutions are random eh :P

All I did was rename the files in "C:\Users\YourUserName\Documents\Sports Interactive\Football Manager 2014\challenges" by adding a ' 1' to the end and bingo bango they showed up.
example 'bottom_division_favourites_english' becomes 'bottom_division_favourites_english 1' . DO NOT RENAME 'CONFIG.XML'!

Hope this helps some other people out!