On the names of DS roms around the website I see (U), (E), (J) and stuff. What does that mean? Will my M3 DS Simply card accept all of those?
it merely indicates which region is from. (U) is USA, (E) is Europe and (J) is Japan. There are other region codes too, used for specific countries (such as (S) for Spain or (I) for Italy for example. This can usually be interpreted to give an idea of language. (U) will usually be english, (E) might be a variety of European languages including English, (J) will be Japanese, and so on. The region code should not affect compatability with your M3
Those indicate which country the ROM is from for lack of a better term. (U) means it's released in the US (E) means it's released in Europe (J) means it's released in Japan I don't think your card would have a problem running any of them. EDIT: Whoops, Loony beat me to it.