Copied directly from the order sheet the dealers used to order a 2001 Boxster S
Cast Light Alloy Wheels "Boxster S Design":
7J X 17 with 205/50 ZR 17 tires, Front
8.5J X 17 with 255/40 ZR 17 tires, Rear
Including anti-theft device

Likewise it could have been ordered with these:

413


Pressure-cast Light Alloy Wheel 18" 'Turbo Look' Wheels
7.5 J x 18 with 225/40 ZR 18 Front
9 J x 18 with 265/35 ZR 18 Rear (Boxster/Boxster S)
10 J x 18 with 265/35 ZR 18 Rear (Carrera)
including anti-theft device.

My justification to stay with 17" wheels... because Porsche says it's the max for 97 due to chassis stiffness, etc. One less thing to worry about!