I’m sure someone else can verify but I don’t think the CD key for a JPN OS will work on an ENG OS. If that is the case, you need to get a CD key and a set of XP Pro discs. Once you re-install the OS you should only have to download a few drivers from Sony’s Website to get you up and running. There isn’t anything too complicated in the unit that requires that many special drivers, as far as I remember most of it was done automatically. The only thing you won’t get is the additional software that came with the unit. I’m not sure how you would go about obtaining those without a restore DVD.
The other route you can try is obtaining a restore DVD from Sony but I’m not 100% sure if you can use it to restore a notebook that doesn’t match the region in the BIOS. I know sometimes it’s locked, sometimes it’s not. Again, maybe someone else can confirm this.
Erik