Hitchhikr has released version 1.01 of PSPTex. PSPTex is a plugin for GIMP 2.2.x allowing you to create textures for the PlayStation Portable.

It can save raw RGBA (5650, 5551, 4444 or 8888) & indexed (T4, T8) textures (with 5650, 5551, 4444 or 8888 palette modes support) as well as DXTC (DXT1, DXT3, DXT5) compresssed ones, it supports the PSP textures swizzle mode and can generate mipmaps, it also have a color key feature to handle transparency and can convert grayscale pictures into alpha channel only textures.

You can download it from here and discuss the plugin in forums here.