Yes, the car is still on the road. I took the pictures this summer. There are other turbo'd Sonetts out there too.
I don't remember much in the way of details, but it involves ALOT of customization. This is not a bolt-on procedure. About the only thing I remember in particular about this car is that he used a Volvo fuel rail.
I think in general you can get plenty of power out of these cars with the usual mods without turbocharging. The driveline can only handle so much and is the real limiting factor.
Atleast you have more room in the engine bay of a 96 vs. the Sonett.
For something totally different, check out this site where someone took a Saab 900 Turbo engine and put it in the back of a Sonett after extensively reworking the sheetmetal. Hope you can read German. I can't...