Ok, i did it.
One last thing, do i need any more code to make it work well on multiplayer too? is WorldSavedData handled ServerSide ?
For others who have the same problem, i advise you to look at these other topics too.
http://www.minecraftforge.net/forum/index.php?topic=6136.0
http://www.minecraftforge.net/forum/index.php?topic=5722.0
http://www.minecraftforge.net/forum/index.php?topic=8264.0
http://www.minecraftforge.net/forum/index.php?topic=6252.0
http://www.minecraftforge.net/forum/index.php?topic=8264.0