because you used vgmtrans and outputted it that way.
Dsbuff to unpack files (or nitro explorer).
If you are just planning to take a look around the game. console tool, crystaltile2, Tinke can all do that. though tinke and CT2 have actual editing functions.
I'd give tinke a try for the sdat stuff.
there are guiides out there for ct2.
tinke not so much (but then I haven't really looked at the wiki yet for it, as I pretty much know what the buttons mean).
You have taken a look at the wiki stickied at the top of this forum right cause if you haven't you should.