@Red: Thank you so much! I've edited skins before, haha. I was really hoping that I could do it! Thanks for the links!
we dont really use the map editor for that, but if you want to put a sprite in game you're going to have to deal with the XNA content pipeline
this is an npc sprite
im sure you immediately get this image so i wont dwell on how it works
once you have your character sprited like this (the dimensions are fixed btw you can't go much higher res than what we're using i'm afraid) you need to compile it into an xnb.
first you'll need xna game studio, its free and you need a free version of microsofts c# ide
visual c# 2010 express
http://www.microsoft.com/visualstudio/eng/downloads#d-2010-express
XNA game studio 4.0 refresh
http://www.microsoft.com/en-us/download/details.aspx?id=27599
then you got 2 options, make a windows game xna project in the IDE and drag the files into a content package and compile it that way, or use xna formatter
http://dracohouston.net/pokemon/tools/xnaformatter/
you need both binaries from that folder, put them in /pokemon/
you'll get a window like this when you run the exe
click the first browse button and find the PNG you want to convert (we are using PNGs as our source images) then you click the second browse button and find the folder you want it to go in. this is /pokemon/content/textures/npcs/ for this job
set the profile to 'reach', this game is a reach spec game, it runs on direct x 9 and shader model 1 so it plays nice on a lot of computers. it doesnt take 'hi-def' profile files for this reason. you should also compress output so the file isnt unnecessarily big.
once the xnb is compiled and in the right place open your character's folder in /pokemon/save/ and open player.dat in a text editor, find the line that says skin and give it the file name of your xnb file. when you load into that save you'll be using your new sprite.
the process is the same for NPC sprites to be added to maps, they are the same format. you can play as any NPC we have sprites for as well, including slenderman
also this is so the wrong forum for this, moving the thread