I lack the time at present to investigate the game so this is going to be a more general post.
You might have picked a hard game but in general there are 3 ways of sprite ripping on the DS.
First things first consider that the DS has a file system much like a optical disc based device and you can usually blow things apart into files. You already discovered crystaltile2 it seems but for the sake of others reading
http://filetrip.net/f23649-CrystalTile2-2010-09-06.html
1) Emulator- not screenshots (although that works) but ram, OAM, BG and VRAM viewers of various flavours.
The game is Dawn of Heroes and it is a really annoying game to hack- it is one of the few that bundles all the files into one massive one (albeit giving you very nice pointers to all of them and little in the way of compression that I can see) but that actually took longer to get into the game and press printscreen than any "hacking" work. Emulation might not be quite up to playing games for fun but hackers and spriters have been using them for years as they do very well for those sorts of things.
You can import save games into most emulators these days as well but that does not stop you from using some basic hacking tricks- maybe not in that example but if you have a game apart you can often rename say the end boss character into a basic enemy or otherwise overwrite it (the DS is quite nice as well as people tend to use resilient coding techniques unlike old consoles that expected so many tiles to be there) and grab your desired sprite from the first level- certainly we use such techniques to rip video and music all the time.
Equally if you look at that some images are composed of layers upon layers (not necessarily ones you can remove with the display layers commands either) and with a bit of fiddling you can send the offending top sprites away from the actual thing you want.
2) File reverse engineering/hardware style viewers- it might be a custom format but chances are it just has the image hastily stuck at the end of the file- you can then line it up and grab your image.
The following image is mainly for an explanation as to how the DS stores and displays imagery at a hardware level- as long as your editor has a 4bpp and an 8bpp GBA viewer you should be good though.
http://gbatemp.net/t73394-gbatemp-rom-hack...st&p=970547 being a copy of the data.
In practice it will probably look more like
http://pix.gbatemp.net/32303/icondemoru9.jpg
or
http://gbatemp.net/pix/32303/gundam.JPG or
http://pix.gbatemp.net/32303/lozdemo.JPG at first but start shifting things around, introduce a proper palette and you get a nice looking image soon enough.
Sometimes games will package new formats in known formats like NARC which you can unpack quite easily to take a look at later things.
3) Existing formats
Crystaltile2 has a bunch of support for this sort of thing but there are a handful of other programs that can do it with
http://gbatemp.net/t162863-susie-plugins-f...tro-rom-file-sy being one of the more interesting and
http://www.romhacking.net/forum/index.php/topic,8407.html being an up and coming tool. Developers can change or badly implement a format though so relying on this method is less than brilliant as it can leave you left hanging for a new game.
General procedure with crystaltile2 is to load the rom in it, press the DS icon to load up the file system viewer and
This way a few clicks (I reckon I could do that in less than 20 and most of those will be double clicks/setup clicks) nets you something like
http://pix.gbatemp.net/32303/gundam2.JPG
Not all games can do this though as they might have unknown files and what have you but if you want some specs for existing formats then
http://www.romhacking.net/docs/%5B469%5Dnds_formats.htm
Guide to crystaltile2
http://gbatemp.net/t73394-gbatemp-rom-hack...p;#entry1310540
Another guide with some good stuff
http://gbatemp.net/index.php?showtopic=291274&hl=
Not all DS sprites are traditional tiled sprites- phoenix wright uses an odd animation/build up technique similar to the bones animation method of 3d.
Speaking of 3d many games will use 3d in lieu of sprites- saves on animation in some ways and works pretty well. Many of Nintendo's first party games and captive devs do this a lot.
Equally nothing stopping you from combining aspects- I am usually far too lazy to find the palette so I will just rip it from an emulator and do any editing using that and you can do things like find the palette in ram and search for that back in the rom (most palettes are either stored together or stored in the same manner for every image in the game)
Compression is also an issue- fortunately not too many games use truly custom stuff and most will be compatible with tools already made. Read the whole thing as it covers a lot of stuff
http://gbatemp.net/t274472-codec-lzss-ds-released
Naturally crystaltile2 has compression support.
