BIG WARNING - This achievement is slightly glitched in that your team has to be at the right level *at the RELEASE DATE* of the game. Some teams have, crucially, changed in levels since then, and if you win with one of those teams, it will NOT count!!!
The one we got caught out on specifically was Azerbaijan, who have changed from 1* to 1.5*, but there may be more. We played all the way through, and... nothing...
There's a full list here, double check this before starting:
http://www.xbox360achievements.org/game/2010-fifa-world-cup/...In terms of method, we use variants of Otilia e Gabita's excellent solution which is highly recommended