Make sure:
1. Your textures isn't there already.
2. Size is 128x128 pixels
3. It is saved in 24bits/pixel without compression
4. It has the same name as your ingame nick with a .tga extension (ie my head texture is called hampa.tga)
5. Note that clan prefixes are ignored so [CLAN]Toribashian gets the Toribashian.tga texture.