Thickness
For both Boxster and Cayman and for years 1997 through at least 2007
As delivered
Minimum before replacement
Front, Base 24mm 22mm
Rear, Base 20mm 18mm
Front, S 28mm 26mm
Rear, S 24mm 22mm
Modern rotors are so thing to save weight (both for unsprung weight's influence on handling and for EPA CAFE reasons) that they are no longer resurfaced, just replaced. Replacing rotors is a relatively easy and straight forward task, just look up the instructions for replacing the pads and you'll see pictures of how to remove the calipers. Once that is done, you replace the rotors and replace the calipers. There is no reason to pay for this to be done if you have average mechanical ability and tools. Also consider eBay as a source of parts. Or ask on the PPBB forum where the current best deals are.
Lots more information on brake parts here.