Yeah, ExCyber is basically right. There's a very similiar approach one can use to find text/graphics in saturn games as opposed to snes. So it wouldn't hurt to consider reading some of the general hacking texts from romhacking.org - Klarth's Console Graphics doc is quite useful.
There's a number of ways to search for text/graphics, though I found the best way is to get an Commlink/AR setup working, start the game in commlink mode, go to the part in the game which has the text you're looking for, then dump the low/high wram and vdp1/vdp2 vram.
Try using tilemod2 plus the various modules I released for it and you -should- be able to find some kind of font. If you do, just open up a hex editor like Hex Workshop, go to the address where the graphics are, copy down about 8 bytes from that area, and either search every file on the disc, or just make an iso and search it instead.
Once you've found the font, the text should be easier. If the text looks like this: http://www.rtpro.yamaha.co.jp/RT/docs/misc/kanji-sjis.html
Then chances are, the text is in shift-jis format. If it looks all random, you'll have to write your own table(see the docs at romhacking.org). Then try doing a relative search based on what you know.
Hopefully one of these days i'll released a number of the saturn specific hacking docs i've been working on. But the most important info for a newbie is still at romhacking.org. Basically once you grasp the basics, the rest is easy enough to pick up(and makes the rest of my documents more relavent).
Lastly, I would suggest you pick a different game for a starting project as iirc DS isn't exactly an easy game to hack.
Cyber Warrior X