so lets say i bought a "x" games from the psn store is it possible to transfer that x game to other memory card or do i have to buy it again and redownload it?
Well the games are stored on the HDD. They're tied to accounts, i think you have to transfer licenses and stuff to redownload them on a different console, not sure though.
I think you can have up to 5 consoles activated on the one account. And yes I think there is a limit on how many times you can download.
That's what you do for the xbox. On the xbox though, you are only alowed to do the license transfer once a year, I'm not sure if it's the same for the playstation.