Requirements:
1-BTX Editor, here's the link: http://dl.dropbox.com/u/3706406/Files/BTX%20Editor.rar
2-Kiwi NDS rom editor: http://dl.dropbox.com/u/3706406/Files/editor.rar
3-Nitro Explorer 2.0b: http://treeki.shacknet.nu/romhacking/NitroExplorer2b.zip
4-A Pokemon HG or Pokemon SS rom (obvious)
5-Microsoft Paint (preferably 2003 version) or any other art creating tool (like adobe photoshop).
Steps:
1-Open your pokemon HG/SS rom with Kiwi's NDS ROM Editor (it'll be called "editor").
2-Extract your ROM by double clicking on the box beside the name of your ROM in the list and then click Extract (the extract Icon looks like a note).
3-Look for where the heck the extracted rom ended up. it will be a folder with the same name as your rom.
4-After finding where it landed (actually, it usually lands in the same area as the rom), open to the folder.
5-Go through these folders: data > a > 0 > 8, and you should find files named from 0 to 9.
6-Drag the file named "1" into the "editor" page...list....box...thingy.
7-The file should appear in the list in the "editor" page, when it does, double click it.
8-Tick the box beside the "1" file in the "editor" window.
9-After that, click the extract button (the note Icon) and yet again, look for where it landed (almost always beside where the file usually is, which is in the folder: pokemon hg/ss folder > data > a > 0 > 8). After finding where it is, remember where it is.
10-Open BTX editor, and click "open BTX file".
11-Go to the folder named "1", and you should find a giant list of files, from 1_000 to 1_862.
12-Select one of those files. some of them won't work, but the rest will.
13-Suprise! the files are the people sprites in the game! It's best that you try opening all of them to find out what each one means. not an important step, but it should answer some problems that might occur, like why the sprite of the trainer on the bike hasn't changed.
14-Just look for the sprite you want to edit. The Main character male sprite is 1_069, and the female one is 1_070.
15-When you find the sprite you want, click "Save png as..." and select a name and save it, but it's best that you save it in a different folder than "1". it might cause problems if you save it in the same folder.
16-Edit the sprite you just saved with something like Microsoft Paint. Skip this step if you wanna use pre-made sprites.
17-After editing the sprites, open BTX editor, open the BTX file of the sprite you chose before, and click "open png".
18-Choose the edited sprites, or in the case of already having pre-made sprites, then choose those ones.
19-Click "Save BTX as..." and go to the "1" folder, and overwrite the BTX file you chose before. it's best that you have a back up of the file just in-case.
20-Open Kiwi's NDS ROM Editor (editor) and click on tools, and then click on "make Narc file".
21-For Source Files Folder, browse the "1" folder. And for Output folder, choose any folder you'd like to make the narc file to. (preferably an empty folder so you won't get confused). Don't tick "Include File Name Table".
22-After that's finished, go to the folder where you made the Narc file to. It should be called "1.narc".
23-Open Nitro Explorer 2, and click on "Load ROM" (the folder Icon). Choose your HG/SS ROM.
24-Open these folders: a > 0 > 8. remember, don't open the data folder. you should, yet again, find files named by numbers from 0 to 9.
25-Click on the "1" File so it becomes highlighted, and then click "Reinsert" (the third Icon from the left, the one that has a picture of a folder and an empty page).
26-Look for the Narc File you made. after you find it, click it and then click open.
27-After a little while, in a small box (it doesn't appear as a window) it will say that it was successfully replaced.
28-Play your HG/SS and you'll notice that the sprite has been changed. Hope I helped! sorry it's so long
