[Edited by Acsuna, 1/31/2009 12:41:54 PM]
The above folder (Vista) holds the games settings and all files can be easily edited via notepad to for example add a custom resolution or tweak your savegame settings.
This value is the amount of "souls" you have, some unlocks can cost 5 million souls so add a high value if you want to unlock everything and be careful about what you unlock as it can affect the game. (Trying to avoid spoilers here so I'm a bit vague.)
This value determines the costume or outfit you have, unsure if there's a bonus by altering the value but the costumes are supposed to either give a damage resistance or a health bonus from what I've read, possible values are 0, 1 or 2 with 1 giving a somewhat more clothed outfit and 2 giving a armored outfit and 0 being the default outfit.
The bought skill and locked skill values determine the skills you have and what's available but I haven't tried editing them yet.
The settings file is useful to give a better resolution instead of the default 1280x1024 one and you can fine tune the various graphical options.