I inserted the Pokemon center into tileset 2 (pallet town) and when I tried to take the tiles that I enserted into tileset 2 I couldn't figure out how to replace my Pokemon center tiles with the original tiles
Okay, I'm going to explain how to do it, and I'll assume you have Advance Map. If you don't, I don't have direct link, but your best bet would be to just get the Pokemon Game Editor by (I believe) Gamer2020, which you can find in the toolbox section, where it is one of the top posts, so it shouldn't be hard to find. Sorry, I can't post a link, but haven't quite gotten to fifteen posts yet :P
Just fire up Advance Map, open your rom, and either go to an existing PC map or to your own PC map (with tilesets 12 and 14 set as tilesets).
There, you'll have to open up the Block Editor (the button that looks like a puzzle piece). Then, on the top menu, you click picture --> save tileset 2. Just give it a name you'll recognize, like PC tileset or something, and save as either .bmp or .dib. After that, you'll want to follow Cello's amazing tutorial, which you'll find slightly towards the bottom of the first page of the Tutorial Section, as I think he explains it better than I ever could (and he has pictures: that helps a lot:P).
Now remember, if you want to easily and exactly replace ALL tiles in the PC with your tiles, without having to do any manual replacing (which mind you, might actually be a good idea, because you might experience some tile errors anyway), you could just search out the PC tiles, and paste your own in the exact location. Personally, I'd just do it the hard way, copy my tiles in the empty room underneath the PC tiles, and then construct my own blocks with that. But that's up to you.
Now, you'll need to remember that inserting tiles isn't enough: Advance Map constructs it's map out of BLOCKS, not tiles. As such, you'll need to either:
A. replace all tiles carefully. If you replace every PC tile with a matching tile of your own (one that would go on the exact same location in a block/map), you won't need to do any block-building of your own. However, as I said, this can be tricky, and I imagine it might lead to block errors.
B. build your own blocks. Slightly (or royally, depends on how much blocks you need to add) tedious, but very effective. This merely requires you to add the tiles to the empty space, after which you'll be able to build your own blocks to your hearts content.
Now, I haven't quite covered everything, probably, so feel free to ask if you still don't get something! (if it's something fairly specific and small, might as well pm me, I'm pretty sure I'll be able to help out)
Hope that was helpful!
@Zupplu
Well, that very much depends on what you want to do. Being fairly new myself, I can't say anything with total certainty, and I honestly don't know anything about DS hacking, but I do know that for GBA, you want to get yourself Advance Map, which you can get (as described above) in the Gamer2020's toolset, Pokemon Game Editor, which has not only two different versions of A-Map, but also a great selection of other tools so you'll be set for a good portion of things you might possibly want to do. Also, I can really advice getting Nameless Sprite Editor 2.X (or NSE 2.X), which lets you edit pretty much all of the pictures in the game. Also, you will need to learn a bit of scripting (because scripting is pretty much what makes anything happen in the game): XSE seems to be standard, and, how nice, it's included in PGE! You might need to look at some tuts though, because I personally didn't find scripting quite self-explanatory. However, a lot can be learned through just looking at stuff through A-Map, so that's always a good place to start :) As for everything else, just take a look around the forums: whatever you want to do, there's probably someone here who's done it, and a good chance there's even an easy tool for it, which let's you do it without having to go through the trouble of ASM, or even Hex editing. For anything more specific, just go ahead and ask away, and good luck hacking!