Dimps (http://www.dimps.co.jp) have redesigned their website and added a separate section for Shin Budokai (http://www.dimps.co.jp/dbz_psp/index.html).
The page contains details of how the system works and news about the Japanese release package - which includes a special Dragon Ball themed PSP pocket.
They're uploading the site on a daily basis, so if there are any extras planned for the JP version they might be added there.
I know this is no big news for US gamers, but for European players, like me, this gives something to look forward to while waiting for the game to be released over here.