I'd suggest the obvious starting point is the OPC with the original number plate details (in case its wearing a private plate now) or use the VIN details off the car itself - I'd anticipate a turbo would probably have been serviced at OPC network dealers across the early years of its life, and their computers all use a central database. I'd expect they should be able to do at least a rudimentary printout of services/dates/mileages for you.
I did it last year when I was selling my Honda, but as I say whet they were able to trace was only rudimentary and listed actual service dates, although as I'd always used the same local dealer they were agreeable to stamping the book for me to bring it up to date, all FOC; whether OPC keep more detailed records, and whether they'd be agreeable to providing a new and stamped service book, I guess you'd have to ask them - I have seen blank service books periodically on eBay if they can't (or won't) supply them. There's one here presently (needs to be posted from the US, but should otherwise be the same)
[link=http://www.ebay.co.uk/itm/2000-Porsche-996-911-Carrera-C2-C4-Owners-Drivers-Manual-Maintenance-Book-G102-/351511229237?hash=item51d7b3b335]http://www.ebay.co.uk/itm...37?hash=item51d7b3b335[/link]
Good luck - let us know how you get on.