The .xml goes into Editor Data.
The .ddt goes into
C:\Program Files\Steam\steamapps\common\football manager 2012\data\db\1220\edt
I'm making a few edits for myself so it starts in 2011 so there are no qualifiers, and no injuries to players .etc
Haven't managed to do it - latest I can get it to start is May 27th 2012