Poking around with JSRF. The tags are in two formats: TGA and PRS. The PRS files look like headerless swizzled pixel data, I'll get back to that. Music is ADX which is to be expected from a Sega game. Most everything else is in a container format. I'm working that out now, looks simple enough.
[Edit] Sounds are XBox ADPCM. Also have the basic container working now. Too bad there's no file names :/