Just in case you still want help, I wrote this up a while ago but never posted it... I might post the full thing later... if it's actually helpful.
Download
this . It is a premade SD pack with a gct (cheat file) already on it for both PAL and NTSC. This has the file replacement code, infite replays, infinite pause camera and tags in replay cheats on it. Next, clear your SD card of everything, unzip the SD pack and copy paste the contense onto your now blank SD card.
Now, download a texture. Make sure you know which character the texture modifies. In the premade SD pack, go to the following directory.
private > wii > APP > RSBE/RSBP (click RSBE if you have the American version, RSBP if you have the PAL version) > pf > fighter
Now, you should be in a folder filled with many other blank folders. Now, each folder responds to a character. Here is what the folders respond to (the characters are listed alphabetically for ease of access;
Character Name | Game Name
Bowser: koopa
Captain Falcon: captain
Charizard: pokelizardon
Diddy Kong: diddy
Donkey Kong: donkey
Falco: falco
Fox: fox
Ganondorf: ganon
Ice Climbers: popo
Ike: ike
Ivysaur: pokefushigisou
Jigglypuff: purin
King Dedede: dedede
Kirby: kirby
Link: link
Lucario: lucario
Lucas: lucas
Luigi: luigi
Mario: mario
Marth: marth
Meta Knight: metaknight
Ness: ness
Olimar: pikmin
Peach: peach
Pikachu: pikachu
Pit: pit
Pokemon Trainer: poketrainer
R.O.B.: robot
Samus: samus
Sheik: sheik
Snake: snake
Sonic: sonic
Wario: wario
Wolf: wolf
Yoshi: yoshi
Zelda: zelda
Zero Suit Samus: szerosuit
Ok, enter the folder of the character who's texture you have. Let's say you have a Roy texture which is fitted to Marth. Your directory would be;
private > wii > APP > RSBE/RSBP (click RSBE if you have the American version, RSBP if you have the PAL version) > pf > fighter > marth
Okay, now that we're in the correct directory, paste in your texture. It is now time to rename your texture. Rename your texture according to which character and which costume you want to modify. If I was modifying Marth and changing his original costume, the name would be FitMarth00. If I was changing Marth's red costume, the name would be FitMarth01. If I was replacing Jigglypuffs original costume, it would be named FitPurin00. Copied below is a list of each character's costume's number (all credit goes to Falco400):
Captain Falcon
00-Original
01-Blood Hawk
02-Green
03-Blue
04-Black
05-Pink
Dedede
00-Original
02-Green
03-White
04-Grayscale
05-Purple
06-Pink
Diddy Kong
00-Original
02-Green
03-Blue
04-Pink
05-Yellow
06-Purple
Donkey Kong
00-Original
01-Red
02-Green
03-Blue
04-Black
05-White
Falco
00-Original
01-Red
02-Green
03-Blue
04-Black
05-Yellow
Fox
00-Original
01-Red
02-Green
03-Blue
04-Black
05-White
Ganondorf
00-Original
01-Red
02-Green
03-Blue
04-Grandpa Ganon
05-Brown
Ike
00-Original
01-Red
02-Green
03-Blue
04-Another Kind Of Green
05-Yellow
Kirby
00-Original
01-Red
02-Green
03-Blue
04-Yellow
05-White
Bowser
00-Original
01-Red
03-Blue
04-Black
05-Pimp Gold
06-Brown
Link
00-Original
01-Red
03-Blue
04-Dark
05-White/Light Blue
06-Yellow
Lucario
00-Original
01-Red
02-Green
04-Light Blue
05-White
Lucas
00-Original
01-Red
02-Green
03-Blue
04-Claus
05-Pink/Purple
Luigi
00-Original
01-Red
02-UNUSED-Blue
03-Blue
04-Fire Luigi
05-Orange
06-Waluigi
Mario
00-Original
02-Green
03-Jumpman
04-Wario
05-Black
06-Fire Mario
Marth
00-Original
01-Red
02-Green
03-Blue
04-Black
05-White
Meta-Knight
00-Original
01-Red
02-Green
03-Blue
04-White
05-Pink
Ness
00-Original
02-Green
03-Blue
04-Bumble-Bee
05-Fuel
06-Mr.Saturn
Peach
00-Original
01-Red
02-Green
03-Blue
04-White
05-Daisy/Yellow
Pikachu
00-Original
01-Cap
02-Bandana
03-Googles
Olimar
00-Original
01-Red
02-Green
03-Blue
04-White
05-Dirty Helmet (Yellow and Black)
Pit
00-Original
01-Red
02-Green
03-Blue
04-Gold
05-Black
Pokemon Trainer
00-Original
01-Red
02-Green
03-Blue
04-Light
Ice Climbers
00-Original
01-Red
02-Green
03-Blue
04-Dark
05-Light
Jigglypuff
00-Normal
01-Flower
02-Sleep Hat
03-Japan Hat
04-Trainer Cap
ROB
00-Original
02-Green
03-Blue
04-Pink/Purple
05-Yellow
06-NES
Samus
00-Original
01-Pink
02-Green
03-Fusion/Blue
04-Gravity Suit/Purple
05-Dark Suit/Black
Zelda
00-Original
01-Red
02-Green
03-Blue
04-Black
05-Ocarina of Time colors
Snake
00-Original
01-Red/Black
02-Green
03-Blue
04-"IDK WTF this is" camo
05-Wild Feline camo
Sonic
00-Original
01-Red
02-Green
04-Gold
05-Black
Toon Link
00-Original
01-Red
03-Blue
04-Purple
05-NES Link
06-Dark
Wario
00-Original (WarioWare)
01-Red (WarioWare)
02-Green (WarioWare)
03-Blue (WarioWare)
04-Black & Red (WarioWare)
05-Orange & Blue (WarioWare)
06-Original (Overall)
07-Red (Overall)
08-Green (Overall)
09-Blue (Overall)
10-WarioLand 2 color (Overall)
11-WarioLand 3 color (Overall)
Wolf
00-Original
01-Red
02-Green
03-Blue
04-Black
05-Red & White
Yoshi
00-Original
01-Red
03-Blue
04-Yellow
05-Pink
06-Light Blue
So, now you're just about ready to start off playing with textures. Stick the SD card into your wii, run it through Gecko OS with orcarina cheats on and viola! You have textures.
NOTE: In some cases when you donwload textures (which are .pcs files) you will also download a .pac file. This .pac file is to maintain the textures during chages (ie. when wario change to wario man or zelda transforms to sheik). Just name the .pac file exactly the same as the original texture and put it in the same directory. You shouldn't have any problems with it.