Well, I probably dont have the latest version. To be fair, Im not 100% sure what version I even have. And Ive been hesitant on upgrading because then Ill have to comb over my quest to look for anything that may have changed.
Are the new versions of ZC located on shardstorm still? I seem to recall the versions on that site were obsoleted.
Err, nope. zeldaclassic.com is once again the hosting location for the up-to-date versions.
If you use 2.53 (the current RELEASE version), you shouldn't experience much in the way of changes since 2.50.2; mostly just numerous bugfixes.
Version 2.55 is also available, but is currently in ALPHA. It is a very stable alpha, but it adds MANY new features. Quests made in any prior version, at least as far back as 1.92 (IIRC), should play as they did in their original versions; we have done a fair amount of backwards-compatibility work. But, you will need to get used to a number of new menus and features if you update to 2.55, which may not be ideal mid-quest. (I would certainly recommend it if you are starting a new quest, as the new features are AWESOME)
Regardless of any of that, I highly recommend using '.ogg' instead of '.mp3'. '.mp3' is terrible. Just don't use it.