How do I get all the brain training games on my DS?

[flirtygerty]

It says on the blurb that there are 'certain conditions' you have to fulfill to get them. Have done the same 3 games loads now & can't work out how to get them. Someone please save my sanity!!

It's based on how many days' stamps you get on the calendar thing. It unlocks a new game every three stamps or so, IIRC.