if they are "free trials" (they should say free trial, normally they are 48 hr trials, but some games have come with 1 month free trials, gta iv comes to mind) then you will want to take both of those codes and just put them inside a game or something untill you need them after you run out of time. but you can buy the one year sub for $29.99 and then redeem the 12 month code and you will have 2 years. free trials will not stack on top of anything, if you have live, and redeem a free trial code you are just wasting it.