Seashore: http://seashore.sourceforge.net/download.php
Once you have it downloaded, open up the folder it created... You should see something like this:

IMPORTANT:
If you do not follow this closely it will not work, I Repeat, NOT WORK!
1. Click and drag Seashore, to your Desktop.
2. Once the Application is on your desktop go to "Show Package Contents" (CTRL + Right Click)
3. Follow this path:
Seashore: Contents > Resources > textures
4. It should look like this with the exception of the 00E folder:

5. I like to create my own folder to put textures in, but thats just me, you could put them into any folder you'd like.
6. Now you can drag or Copy and paste textures in that folder, from anywhere.
7. You could get them off the internet, In the contents of TT you could use Terrains for skins, shapes for skins, even skies for skins! I don't care.
8. IMPORTANT: Do NOT change the .jpg to .png or a .png to a .jpg, if you do, the application will randomly shut down!
I hope this helps out with all of you TT skinners! I hope this helps everyone out considering it took me quite a while to write this! AGain I hope this helps and contact me if you have any questions, I'd be more than glad to help!
-00E