How exactly did you install the new OS? Did you format the drive as part of the install?
If you have a clean XP install that went onto an empty HD, then the proper XP sound card drivers that match the OS (UK drivers for UK XP, Japanese drivers for Japanese XP) shouldn't cause a crash. Try deleting the sound card in device manager, reboot and let XP find it again, and install the proper drivers. If that doesn't work, double check you have the proper drivers, and if so I'd suggest a different sound card.
If OTOH you put the new XP into the existing Windows folder on the HD, all bets are off. In this case, there's a slim chance you may have a restore point from the Japanese install, and perhaps you could get it back with system restore. But don't count on it. Best bet is to format the drive and install from scratch. I'd suggest getting the keyboard first - I've never tried to install a non-Japanese XP with a Kanji keyboard and wonder if the install would break when it gets to the part about keyboard layout.